Image forming apparatus, drum unit, image forming module, and method of insertion and removal of a damper into and from an image carrier drum

ABSTRACT

An image forming apparatus includes a photoreceptor belt formed by either a belt or a thin-walled cylinder. A charging unit that sets bias characteristics of the photoreceptor belt has an arrangement to approach towards the photoreceptor belt. A damper is provided on a side of the photoreceptor belt opposite to the side facing the charging unit. The damper absorbs vibrations in the photoreceptor belt through a supporting plate.

BACKGROUND OF THE INVENTION

[0001] 1) Field of the Invention

[0002] The present invention relates to a technology for preventingnoise caused by vibrational resonance produced in a latent image carrierdue to a thin-walled structure of an image forming apparatus.

[0003] 2) Description of the Related Art

[0004] In image forming apparatuses like a copying machine, a facsimile,a printer, and a printing machine, steps of charging, writing,developing, and transferring are carried out for a photoreceptor as alatent image carrier. In the step of transferring, a toner image that istransferred on a recording medium like a recording paper is fixed togive a copy or a printout.

[0005] A structure that employs a non-contact charging method withaerial discharge using a corona charger is used for charging of thephotoreceptor. However, in the structure, discharge products like ozoneand nitrogen oxide are generated during discharging which may result indeterioration of environment or deterioration of chargingcharacteristics on the photoreceptor. Therefore, a contact chargingmethod, which does not generate the problems and enables to apply lowvoltage, is proposed as a substitute for an aerial discharge. Astructure that injects charge by applying voltage between thephotoreceptor and any one of a brush, a roller, and a blade of aconductive material that is kept in contact with the photoreceptor isknown as one of the contact charging methods.

[0006] In the contact charging method, it is possible to apply lowvoltage and there is no generation of discharge products. However, sinceany one of a brush, a roller, and a blade made of a conductive materialis in direct contact with the photoreceptor, it is easy to carry outreverse transition of deposits of toner etc. that remain on thephotoreceptor. The deposits that have undergone reverse transitionhinder the injection of charge and may deteriorate the chargingcharacteristics. Furthermore, when a charging member is left withoutbeing used in a charging process for hours, a portion of the chargingmember that is in contact with the photoreceptor, changes shape due topermanent deformation. As a result, when the charging process is carriedout again, there is no uniform contact of the charging member with thesurface of the photoreceptor, which may result in charging unevenness.

[0007] To solve this problem, a unit that forms a charging range betweenthe photoreceptor and the charging member is proposed. The chargingmember is disposed so that a prescribed minute interval is maintainedbetween the photoreceptor and the charging member. The unit is anintermediate structure of non-contact and contact charging methods. Acharging method (proximity charging method) has been employed in recentyears. In this method, a prescribed minute interval is provided betweenthe photoreceptor and the charging member such as a brush, a roller, anda blade of a conductive material, and charging is carried out byapplying either of only dc voltage and dc voltage superimposed by an acvoltage.

[0008] In a structure which employs the proximity charging method, in acase where the charging member is a roller, a film of prescribedthickness is wound on both ends of the charging roller in its axialdirection for setting of a gap and size of the minute gap is prescribedby thickness of the film.

[0009] Maintaining the prescribed size of the minute gap is an importantcondition to have no variation in the charging characteristics. When itis assumed that the size of the minute gap is maintained, the uniformcharging becomes possible by applying of dc voltage for which setting iscomparatively easy. However, when the size of the gap variesconsiderably, there is a considerable variation in a charging electricalpotential in proportion to the variation in the size of the gap.Therefore, conventionally, various ideas have been thought up to achieveuniform charging characteristics even in a case where the size of thegap is varied by superimposing ac voltage on dc voltage.

[0010] On the other hand, apart from the charging unit, a developingunit is there to set the charging characteristics, i.e. biascharacteristics. In a case of the developing unit, a developing methodthat uses either of a one-component developer and a two-componentdeveloper, is known. In the developing unit which uses the two-componentdeveloper, a developer that includes a carrier made of a magneticmaterial (substance) for an insulating toner, is agitated by anagitator. The toner is then deposited by charging on the carrier and thedeveloper is made to be in contact with the photoreceptor.

[0011] In a developer carrier used in the developing unit, a developingsleeve, which can carry the developer on its surface, is used and amagnetic roll with a plurality of south poles and north poles lined upalternately on it is provided inside the developing sleeve. In thedeveloper carrier, the developer is drawn up by magnetic force of themagnetic roll and a magnetic brush is formed by making the developererected in the form of a brush on the surface of the developer carrier.

[0012] When the magnetic brush carried on the surface of the magneticsleeve comes in contact with the electrostatic latent image that isformed on the photoreceptor based on either of image information and apaper document image, a developing bias is applied between thephotoreceptor and the magnetic sleeve as the developer carrier. Due tothe developing bias, the toner in the magnetic brush undergoeselectrostatic absorption by the electrostatic latent image therebyforming a toner image.

[0013] As a developing bias, a bias as follows is used. The biassuperimposes the ac voltage on the dc voltage to improve the developingcapability, carry out the developing to the electrostatic latent imageidentically with utmost clarity, and improve uniformity of dots.Moreover, the bias has a first peak value V1 for transferring the tonerfrom the developer carrier to the photoreceptor and a second peak valueV2 for transferring the toner from the photoreceptor to the developercarrier. A method using the bias as a developer bias, in which avibrating electric field is created in a developing area between thedeveloper carrier and the photoreceptor and charged toner is applied onthe photoreceptor, is known.

[0014] For the ac voltage which is superimposed on dc voltage, arectangular waveform as in FIG. 44, a sine waveform as in FIG. 45, atriangular waveform as in FIG. 46, or a duty bias as shown in FIG. 47 isused.

[0015] In a case of using the duty bias shown in FIG. 47, a ½ value ofthe waveform differs from an average value of time integral. In FIG. 47,such a bias as follows is used. That is, the bias includes a timerequired for application of the first peak value V1 and a time requiredfor application of the second peak value V2. At the first peak value V1,an electric field is created such that the electric field is biased in adirection in which the toner is transferred from the developing sleeveto the photoreceptor. At the second peak value V2, an electric field iscreated such that the electric field is biased in a direction in whichthe toner is transferred from the photoreceptor to the developingsleeve.

[0016] In a case of using the duty bias, by optimizing a frequency of acvoltage, a duty ratio (=t1/(t1+t2)×100% in FIG. 47), and a peak-to-peakvalue i.e. a difference between a maximum value of ac voltage (V1) and aminimum value of ac voltage (V2), it is possible to deposit the tonerefficiently on an image area of the photoreceptor or not to deposit thetoner on non-image area of the photoreceptor. Moreover, the optimizationalso enables the adjustment for increasing the density of an image whileimproving the uniformity of toner dots identical to the latent image.

[0017] Among methods which use the other developer i.e. theone-component developer, a jumping developing is a known method. In thejumping developing, an electrostatic latent image on the photoreceptoris developed while the developing sleeve as the developer carrier of thedeveloping unit and the photoreceptor are maintained in the non-contactstate. In the jumping developing, a layer of the one-component developeris formed on the developing sleeve. More specifically, a magnetic rollhaving a plurality of south poles and north poles lined up alternatelyon it and facing the electrostatic latent image carrier, is fixed on thedeveloping sleeve. Furthermore, a toner brush is formed in a developingarea and the developer (toner) is splashed and applied on thephotoreceptor by applying a developing bias obtained by superimposing anac component on a dc component, to the developing sleeve. Fogged toneris then returned in the direction of the developing sleeve and thelatent image is visualized as a toner image.

[0018] When the developer is a one-component developer, in the samemanner as the two-component developer, the developing bias method isused. In the developing bias method, by varying the peak-to-peak value,frequency, and duty ratio, it is possible to deposit the tonerefficiently on the image area of the photoreceptor or not to deposit thetoner on the non-image area of the photoreceptor. Moreover, the imagedensity is increased while improving the uniformity of toner dots.

[0019] Depending on a setting of the bias characteristics that iscarried out in the charging unit and the developing unit, noise iscaused by applying ac voltage during shifting of the photoreceptor.Following is a reason for the generation of noise. A lighter weightconductive material in cylindrical form is used for the photoreceptor.Concretely, an aluminum cylinder having thin walls is used for thephotoreceptor with a structure that resonates easily. Besides, not onlyunits used in charging and developing processes are disposed facing thephotoreceptor, but units for carrying out writing, transferring, andcleaning processes are also disposed facing the photoreceptor. Inparticular, the unit that carries out the cleaning process is disposedclose to the photoreceptor, other than the units for charging processand developing process. Therefore, the photoreceptor can resonate easilydue to vibrating electric field created when ac voltage is applied.Furthermore, due to a cleaning blade of the cleaning unit that is incontact with the photoreceptor, the vibrations are generated in thethin-walled cylinder due to repetition of deformation and restoration ofshape of the cleaning blade when the cleaning blade scrapes thephotoreceptor, and resonance in the photoreceptor produces noise.

[0020] That is, the image forming apparatuses like a copying machine, aprinter, a facsimile, or a multifunction machine including any functionsof these have been known widely. The image carrier drum includes eitherof a photoreceptor drum on surface of which a toner image is formed bycharging, exposing, and developing and an intermediate transfer drum onsurface of which a toner image is transferred from the photoreceptor andformed. The image carrier drum vibrates due to an external force thatimparts vibrations, thereby resulting in generation of noise from theimage carrier drum. For example, image forming units like a chargingunit and a cleaning unit are provided around the photoreceptor drum. Thecharging member vibrates due to effect of ac voltage applied to thecharging unit. The charging member vibrates due to stick-slip which iscaused by the cleaning blade that is in pressed contact with the surfaceof the image carrier drum. The stick-slip starts as the image carrierdrum rotates. The vibrations are transmitted to the image carrier drumto make the image carrier drum vibrate, and to thereby generate noise. Auser may feel unpleasant because of noise. Therefore, measures have beentaken in conventional techniques by providing the damper inside theimage carrier drum to minimize vibrations of the image carrier drum toreduce the noise.

[0021] On the other hand, an image forming apparatus explained below hasbeen in practical use to enable conservation of energy. The imageforming apparatus uses a toner having a low melting point, and isstructured such that a transferred toner image can be fixed on therecording medium at comparatively low temperature. However, a case ofusing the toner having a low melting point tend to generate noise easilyas compared to a case of using a toner having a high melting point.Therefore, it is found that the conventional damper is unable to reducethe noise sufficiently. It is not sure that the use of the toner havinga low melting point increases the noise. However, additives like wax orthe like contained in the toner tend to stick to the surface of theimage carrier drum. Since the amount of the additive that is depositedbecomes non-uniform depending on an image pattern, a component like thecleaning blade in contact with the surface of the image carrier drumdoes not move uniformly. It is considered that loud noise that isgenerated in the image carrier drum is due to vibrations caused bynon-uniform movement of the cleaning blade.

[0022] A structure in which the photoreceptor is made solid i.e. a solidcylinder has been disclosed, for example, in Japanese Patent ApplicationLaid Open Publication (“JPA”) No. HEI 07-72641, as the conventionalstructures to reduce the noise. Furthermore, a structure in which atleast two of an elastic body and a cylinder member are fitted inside thephotoreceptor and resonance in peripheral wall of the thin-walledcylinder is reduced has been disclosed in JPA No. HEI 11-184308, for thesame purpose.

[0023] Moreover, there is another structure made by using a cylinderunit in which the damper is inserted inside the cylinder to reducevibrations of the cylinder and therefore the noise is minimized. Thistype of structure has been disclosed in JPA No. HEI 11-35167 and JPA No.HEI 10-97158.

[0024] In recent years, products which can be recycled are promoted withan object of protection of environment and saving of resources. Samething is expected about the cylinder unit. To have better recycling of aproduct formed by a plurality of components, it is necessary that theproduct be structured in such a way that each component of the productcan be dismantled easily after the product is used and the dismantledcomponent can be reused or can be reprocessed. However, in theconventional cylinder unit, the damper inserted inside the cylinder isfixed to the cylinder and therefore it is difficult to remove the damperfrom the cylinder. Thus, the conventional cylinder unit is founddifficult to be recycled.

[0025] However, in the structure for prevention of noise, increase incost of the photoreceptor and complications in structures are matters ofconcern. When the photoreceptor is structured using a solid body, it notonly raises the cost but also increases weight. Due to increase in theweight, there is an increase in driving force required for rotation,which results in increase in inertial force. The increase in weight ofthe photoreceptor affects its portability, which may result in damagingthe surface of the photoreceptor or causing an injury to a person due toheavy weight on dropping of the photoreceptor during replacement job. Ifa plurality of damping structures are provided inside the photoreceptor,there is a rise in cost due to the increased number of components andassembling processes.

[0026] Moreover, the image forming apparatus that uses the toner havinga low melting point tends to generate noise easily as compared to thecase of using the toner having a high melting point. Therefore, theconventional damper is unable to reduce the noise sufficiently.

SUMMARY OF THE INVENTION

[0027] It is an object of the present invention to solve at least theproblems in the conventional technology.

[0028] According to one aspect of this invention, an image formingapparatus includes a latent image carrier that includes an arrangementof any of a belt and a thin walled hollow cylinder, the latent imagecarrier having a first surface and a second surface. The apparatus alsoincludes a bias applying unit that has an arrangement for approachingtowards the first surface of the latent image carrier, in which the biasapplying unit sets bias characteristics of the latent image carrier. Theapparatus further includes a vibration absorber that absorbs vibrationsin the latent image carrier, in which the vibration absorber is made totouch the second surface of the latent image carrier.

[0029] According to another aspect of this invention, an image formingapparatus includes a toner image forming unit that forms a toner imageon an image carrier drum using a toner having an outflow starttemperature less than or equal to 102° C. measured by flow testermethod. The apparatus also includes a damper provided inside the imagecarrier drum, in which the damper is made of a material with a tangentof loss tan δ of the damper is greater than or equal to 0.5. The tangentof loss is a value of damping effect.

[0030] According to still another aspect of this invention, a drum unitincludes a cylinder, a shaft that extends inside and supports thecylinder, and a damper disposed inside the cylinder. The cylinder, theshaft, and the damper are assembled such that when the shaft is pulledout from the cylinder, the damper moves in the axial direction of thecylinder together with the shaft and is removed from the cylinder.

[0031] According to still another aspect of this invention, an imageforming module includes an image carrier drum, and a shaft that extendsinside and supports the drum. The module also includes a damper disposedinside the drum, in which the drum, the shaft, and the damper areassembled such that when the shaft is pulled out from the drum, thedamper moves in the axial direction of the drum together with the shaftand is removed from the drum. The module further includes an imageforming element that forms an image on the drum. The image carrier drumand the image forming element are assembled together as an integratedassembly.

[0032] According to still another aspect of this invention, the imageforming apparatus includes an image carrier drum, a shaft that extendsinside and supports the drum, and a damper disposed inside the drum. Thedrum, the shaft, and the damper are assembled such that when the shaftis pulled out from the drum, the damper moves in the axial direction ofthe drum together with the shaft and is removed from the drum.

[0033] According to still another aspect of this invention, a method ofinsertion and removal of a damper into and from an image carrier drumincludes inserting the damper into the image carrier drum from anopening on one end in an axial direction of the image carrier drum andthereby mounting the damper inside the drum. The method also includesremoving the damper from an opening on other end in the axial directionof the image carrier drum.

[0034] According to still another aspect of this invention, a drum unitincludes an image carrier drum, and a damper. The damper is insertedinto the image carrier drum from an opening on one end in an axialdirection of the image carrier drum to thereby mount the damper insidethe drum, and the damper mounted inside the drum is removed from anopening on other end in the axial direction of the image carrier drum.

[0035] According to still another aspect of this invention, an imageforming module includes a drum unit having an image carrier drum and adamper, in which the damper is inserted into the image carrier drum froman opening on one end in an axial direction of the image carrier drum tothereby mount the damper inside the drum, and the damper mounted insidethe drum is removed from an opening on other end in the axial directionof the image carrier drum. The module also includes an image formingunit that forms a toner image on the image carrier drum. The drum unitand the image forming unit are detachable from a main body of the imageforming apparatus.

[0036] According to still another aspect of this invention, an imageforming apparatus includes an image forming module. The image formingmodule includes a drum unit having an image carrier drum, and a damper,in which the damper is inserted into the image carrier drum from anopening on one end in an axial direction of the image carrier drum tothereby mount the damper inside the drum, and the damper mounted insidethe drum is removed from an opening on other end in the axial directionof the image carrier drum. The apparatus also includes an image formingunit that forms a toner image on the image carrier drum. The drum unitand the image forming unit are detachable from a main body of the imageforming apparatus.

[0037] According to still another aspect of this invention, an imageforming apparatus includes a drum unit having an image carrier drum toform a toner image and a damper. The damper is inserted into the imagecarrier drum from an opening on one end in an axial direction of theimage carrier drum to thereby mount the damper inside the drum, and thedamper mounted inside the drum is removed from an opening on other endin the axial direction of the image carrier drum.

[0038] The other objects, features and advantages of the presentinvention are specifically set forth in or will become apparent from thefollowing detailed descriptions of the invention when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a schematic diagram of an image forming unit in an imageforming apparatus according to a first embodiment of the presentinvention;

[0040]FIG. 2 illustrates a roller around which a photoreceptor belt usedin the image forming unit shown in FIG. 1 is wound;

[0041]FIG. 3 illustrates another structure of the roller shown in FIG.2;

[0042]FIG. 4 illustrates still another structure of the roller shown inFIG. 2;

[0043]FIG. 5 illustrates still another structure of the roller shown inFIG. 2;

[0044]FIG. 6 illustrates a structure for prevention of noise in theimage forming apparatus shown in FIG. 1;

[0045]FIG. 7 illustrates another example of the structure for preventionof noise shown in FIG. 6;

[0046]FIG. 8 illustrates a photoreceptor belt used in the image formingapparatus shown in FIG. 1;

[0047]FIG. 9 illustrates another example of the image forming apparatus;

[0048]FIG. 10 illustrates a developing unit used in the image formingapparatus shown in FIG. 9;

[0049]FIG. 11 illustrates a latent image carrier used in the imageforming apparatus in FIG. 9;

[0050]FIG. 12 illustrates another structure of the latent image carrierused in the image forming apparatus in FIG. 11;

[0051]FIG. 13 is a graphical of noise characteristics in the structureof the latent image carriers shown in FIG. 11 and FIG. 12;

[0052]FIG. 14 illustrates an application related to the image formingapparatus;

[0053]FIG. 15 is a schematic diagram of an image forming unit in animage forming apparatus according to a second embodiment of the presentinvention;

[0054]FIG. 16 is a longitudinal cross section of an image carrier drumwith a damper disposed inside the drum;

[0055]FIG. 17 is a longitudinal cross section of a damper which isdifferent in shape than the damper in FIG. 16;

[0056]FIG. 18 illustrates a charging roller that is in contact with asurface of the image carrier drum;

[0057]FIG. 19 illustrates a charging unit formed by a brush roller;

[0058]FIG. 20 illustrates a charging unit formed by a magnetic brushunit;

[0059]FIG. 21 is a schematic diagram of an image forming unit in animage forming apparatus according to a third embodiment of the presentinvention;

[0060]FIG. 22 is a longitudinal cross section of a cylinder unit in FIG.21;

[0061]FIG. 23 is an exploded perspective view of an image carrier drumand a flange in FIG. 22;

[0062]FIG. 24 is a cross section of a state when a shaft and a damperare moved from the state shown in FIG. 22;

[0063]FIG. 25 is a cross section of another example of the damper;

[0064]FIG. 26 is a cross section of still another example of the damper;

[0065]FIG. 27 is a cross section of still another example of the damper;

[0066]FIG. 28 is a cross section of still another example of the damper;

[0067]FIG. 29 is a cross section of a cylinder unit in which a flangehaving a first cylinder member and a second cylinder member is used;

[0068]FIG. 30 is a perspective view of the first and the second cylindermembers;

[0069]FIG. 31 is a cross section of a state while the first and thesecond cylinder members are assembled with the image carrier drum;

[0070]FIG. 32 is a schematic diagram of an image forming unit in animage forming apparatus according to a fourth embodiment of the presentinvention;

[0071]FIG. 33 is a longitudinal cross section of a drum unit in FIG. 32;

[0072]FIG. 34 is a cross section of a state before the damper isinserted into the image carrier drum;

[0073]FIG. 35 is a cross section of a state after the damper is insertedinto the image carrier drum;

[0074]FIG. 36 is a cross section of a state when the damper has come incontact with the flange;

[0075]FIG. 37 is a cross section of a state when the damper is pushedout further after the flange is removed from the image carrier drum;

[0076]FIG. 38 is a cross section of an example of inserting and removingthe damper into and from the image carrier drum by pulling the damper bya force imparting member;

[0077]FIG. 39 is a longitudinal cross section of another example of thedrum unit;

[0078]FIG. 40 is a cross section of a state after the shaft and thedamper are moved from positions shown in FIG. 39;

[0079]FIG. 41 is a cross section of a drum unit in which the damper isformed by a compression coil spring;

[0080]FIG. 42 is a cross section of an example of using the flangehaving a first and a second flange members;

[0081]FIG. 43 is schematic cross section of another example of the imageforming apparatus;

[0082]FIG. 44 is a graph of an example of a developing bias;

[0083]FIG. 45 is a graph of another example of the developing bias;

[0084]FIG. 46 is a graph of still another example of the developingbias; and

[0085]FIG. 47 is a graph of still another example of the developingbias.

DETAILED DESCRIPTION

[0086] Exemplary embodiments of an image forming apparatus, a drum unit,an image forming module, and a method for insertion and removal of adamper into and from an image carrier drum are explained in detail belowwith reference to the accompanying drawings. The present invention isnot limited only to the following embodiments.

[0087]FIG. 1 is a schematic diagram of an image forming unit of an imageforming apparatus 100 according to a first embodiment. In the imageforming apparatus 100, a photoreceptor that functions as a latent imagecarrier, is formed by a belt (hereinafter, “photoreceptor belt 101”).The photoreceptor belt 101 is wound around among a plurality of rollers102 to 104 and can move in a direction indicated by an arrow A. Acharging unit 105, a writing unit 106 (in FIG. 1, only optical path isshown), a developing unit 107, a transferring unit 108, and a cleaningunit 109 are disposed around the photoreceptor belt 101 along thedirection of movement of the belt to carry out image forming processing.

[0088] The rollers 102 to 104 are arranged such that the photoreceptorbelt 101 forms a triangle turned upside down as shown in FIG. 1 and avertex of the triangle is a transferring position.

[0089] The charging unit 105 is one of the units which sets biascharacteristics in the photoreceptor belt 101. As shown in FIG. 1 andFIG. 2, the charging unit 105 is a unit adopting a non-contact methodand has a charging roller 105A provided close to the photoreceptor belt101 maintaining a prescribed gap (G) that is set. Both ends of a shaft105B of the charging roller 105A in its axial direction are biased by anelastic body 105C like a spring etc. towards the photoreceptor belt 101.A displacement caused by the biasing is regulated by an abutting member105D that includes a film wound around both ends in the axial directionof the charging roller. The abutting member 105D protrudes from theperipheral surface of the charging roller 105A towards the photoreceptorbelt 101.

[0090] In the embodiment, the prescribed gap (G) maintained by theabutting member 105D is set according to the type of a developer that isused in the developing unit 107. In the case of the one-componentdeveloper that uses only magnetic toner as developer, the gap is lessthan or equal to 300 μm and in the case of the two-component developerwith toner and magnetic carrier that are mixed, the gap is less than orequal to 500 μm. The pushing by the elastic body 105C maintains the gap.The difference in the gap is irrespective of the developer that is used,and prevents deterioration of the developing capability when dc and acvoltages are applied.

[0091] Direct voltage is applied to the charging roller 105A via theprescribed gap G defined by the abutting member 105D due to constantvoltage control of dc −700V through a control circuit (not shown). Atthe same time, alternate voltage is applied due to low current controland an aerial discharge is carried out to the photoreceptor belt 101.Thus, the photoreceptor belt 101 is charged uniformly.

[0092] When the photoreceptor belt 101 charged uniformly by the chargingunit 105 moves, the writing unit 106 carries out optical writing. Anelectrostatic latent image according to either of image information anda paper document image, is formed due to the optical writing. Theelectrostatic latent image is processed to form a visualized image by adeveloper (toner), which is supplied by the developing unit 107. Thevisualized toner image is transferred on a recording paper S that is fedby a paper-feeding unit not shown. The image is transferred on the paperby the transferring unit 108 that includes a transfer roller providedagainst the roller 103 that is at the vertex of the lower part of thetriangle formed by the photoreceptor belt 101. The transferred tonerimage is fixed on the recording paper S by a fixing unit (not shown),and discharged. The cleaning unit 109 removes residual toner andresidual charge on the photoreceptor belt 101, after transferring of theimage. The photoreceptor belt 101 moves again toward the charging unit105, thereby preparing for the next image forming.

[0093] The structure of the charging unit 105 is not restricted only toa non-contact roller with respect to the photoreceptor belt 101. Astructure that has a roller in contact with the photoreceptor belt 101,a structure that uses a conductive brush as a charging member, and evena magnetic brush that uses magnetic particles, can be used.

[0094]FIG. 3 illustrates a supporting structure of the photoreceptorbelt 101. The photoreceptor belt 101 is wound around among the rollers102 to 104. The roller 102 facing the charging unit is provided with avibration absorber 110 on the surface of the roller 102. The vibrationabsorber 110 uses a strong vibration absorbing material 110A thatcontains an elastic material like butyl rubber or nitrile rubber.

[0095] The structure of the vibration absorber 110 can be varied bysubstituting the vibration absorber provided on the roller 102 by eitherof structures as follows. One of the structures has a strong vibrationabsorbing material 110B in form of a solid block which is press fittedin the hollow cylindrical roller 102 as shown in FIG. 4. The otherstructure has a strong vibration absorbing material 110C in form of ablock with a hollow inside of the block as shown in FIG. 5. In anystructure of the vibration absorber 110, the elastic body made by eitherof butyl rubber and nitrile rubber is used. The vibration absorber 110is provided in either of an axial direction of the roller 102 where theabsorber tends easily to deform by bending and an area around this axialdirection.

[0096] Tangent of loss tan δ for any of the strong vibration absorbingmaterial 110A or the strong vibration absorbing blocks 110B and 110C, isset to be greater than or equal to 0.5. The tangent of loss tan δ meansa tangent of a phase angle δ (loss angle) of stress and strain in thematerial used as the strong vibration absorbing material 110A or thestrong vibration absorbing material blocks 110B and 110C. Value tan δdenotes intrinsic damping effect value of the material, and the greaterthe value of tan δ, the greater the damping effect is. Therefore, in theembodiment, generation of harsh noise is minimized by at least makingthe value of tangent of loss tan δ greater than or equal to 0.5irrespective of use of the strong vibration absorbing material 110A andthe strong vibration absorbing blocks 110B and 110C. The results ofexperiment regarding the settings of loss value tan δ are mentioned inthe latter part.

[0097] When dc voltage and in addition ac voltage are applied to thecharging unit 105 as one of the units for setting the biascharacteristics, the photoreceptor belt 101 that corresponds thethin-walled member, resonates due to the vibrating electric field in thecharging unit 105.

[0098] Since the resonance produced in the photoreceptor belt 101 isreduced due to absorption of vibrations by the roller 102 that is incontact with the photoreceptor belt 101, the resonance in thephotoreceptor belt 101 is suppressed, thereby preventing noise caused bythe resonance. The photoreceptor belt 101 in particular, which is athin-walled structure, tends to resonate easily. However, when thephotoreceptor belt 101 resonates, the resonance is controlled by avibration absorbing function of the vibration absorbing material 110A orthe vibration absorbing materials 110B and 110C which function asvibration absorber 110 when resonance is produced, there is almost nogeneration of noise.

[0099] As a modification of the structure in the embodiment, a driveroller of the photoreceptor belt 101 may be used as a roller providedwith the vibration absorber 110. In this case, to transmit the drivingforce from the drive roller to the photoreceptor belt 101, the vibrationabsorber 110 is provided on the drive roller that is in stronger contactwith the photoreceptor belt as compared to the contact of the otherroller with the photoreceptor. By providing the vibration absorber 110in the drive roller, the resonance produced in the photoreceptor belt101 can be dealt with in the most effective manner and can be reducedefficiently.

[0100] Following is an explanation of another example in which avibration absorption function is provided for the photoreceptor belt101. FIG. 6 illustrates a structure in which the vibration absorber 110is provided on a supporting plate 111 that is provided on an inner sideof the photoreceptor belt 101. The supporting plate 111 functions as aguide for the photoreceptor belt 101. The supporting plate 111 is a flatplate made of hard material and the vibration absorber 110 is providedon the side of the supporting plate 111 opposite to the side thereofthat faces the photoreceptor belt 101.

[0101]FIG. 7 illustrates a structure in which the charging unit 105 asone of the units for setting the bias characteristics in FIG. 6 isdisposed in a position opposite to the supporting plate 111 sandwichingthe photoreceptor belt 101. In this case also, the vibration absorber110 is provided on the side of the supporting plate 111 opposite to theside thereof that faces the photoreceptor belt 101.

[0102] According to the first embodiment, vibrations generated in thecharging unit 105 when the bias is superimposed with the ac and dcvoltages respectively by the charging unit 105 are propagated to thephotoreceptor belt 101. When the vibrations are propagated, thephotoreceptor belt 101 starts resonating. By propagating the resonanceto the supporting plate 111 that is in contact with the photoreceptorbelt 101, the vibration absorber 110 absorbs the resonance. Thus, theresonance in the photoreceptor belt 101 is minimized thereby preventingthe generation of noise.

[0103] Following is an explanation of a structure in which thephotoreceptor belt 101 itself prevents. FIG. 8 is a cross section of thephotoreceptor belt 101. The photoreceptor belt 101 is structured bysuperimposing a photosensitive layer 101B on a surface of a substrate101A made of a thin metal foil or the like. On the opposite side of thephotosensitive layer 101B beyond the substrate 101A is the vibrationabsorber 110 that is formed by an elastic body using either of a butylrubber and nitrile rubber.

[0104] The vibration absorber 110 is provided on the side opposite tothe photosensitive layer 110B via the substrate 101A, and thereforevibrations in the photoreceptor belt 101 are minimized due to absorptionby the vibration absorber 110 thereby minimizing resonance in thephotoreceptor belt and preventing the noise.

[0105] Why the vibrations are produced in the charging unit 105 has beenexplained above. The cleaning unit 109 provided with the cleaning bladeis a unit that generates vibrations while being in contact with thephotoreceptor belt 101. Vibrations caused by deformation due to scrapingof the cleaning blade and by scraping during restoration of the shapeafter deformation, are also absorbed in the same manner as absorption ofthe resonance produced by the charging unit 105. The image formingapparatus in the invention includes a copying machine, a printer, afacsimile, and a printing machine.

[0106] Following is an explanation of still another embodiment of thepresent invention. FIG. 9 is a schematic diagram of an image formingapparatus according to another embodiment. An image forming apparatus 20in FIG. 9 is a copying machine in which a thin-walled cylinder is usedas a latent image carrier and plurality of the latent image carriers areprovided to allow image formation of plural colors. The image formingapparatus 20 in FIG. 9 employs a method of transferring an image of eachcolor separation to the same intermediate transfer body one afteranother and performing collective transfer of the images superimposed onthe intermediate transfer body to a sheet like recording medium such aspaper.

[0107] The image forming apparatus 20 includes units as follows. Theunits include image forming units 21C, 21Y, 21M, and 21BK that formimages of each color according to an image on a document. The units alsoinclude a transferring unit 22 that is disposed opposite to the imageforming units 21C, 21Y, 21M, and 21 BK. The units further include amanual feed tray 23 and a paper feeding cassette 24 as sheet-like mediumfeeding units for feeding a sheet-like recording medium to each transferarea where the image forming units 21C, 21Y, 21M, and 21BK and thetransferring unit are disposed opposite to each other. The units furtherinclude register rollers 30 that feed a recording medium according totiming of image forming by the image forming units 21C, 21Y, 21M, and21BK after transferring from the manual feed tray 23 and the paperfeeding cassette 24. The units further include a fixing unit 1 thatcarries out fixing on the recording medium after the image istransferred in the transfer area.

[0108] In the image forming apparatus 20, any of sheet-like recordingmedia can be used as a sheet-like medium. The sheet-like recordingmedium includes an ordinary paper used for copy in general (hereinafter“ordinary paper”), an OHP sheet, a 90K paper like a postcard and a card,a cardboard of basis weight greater than or equal to 100 g/m² and anenvelope that are so-called special purpose sheets having a heatcapacity more than that of the above types of sheets (hereinafter,simply referred to as “special purpose sheet”).

[0109] The image forming units 21C, 21Y, 21M, and 21BK carry outdeveloping of cyan, yellow, magenta, and black colors respectively.Although the toner color handled by each image forming unit isdifferent, the structures of the units are the same. Therefore, thestructure of the image forming unit 21C, as a representative of theimage forming units 21Y, 21M, and 21BK, is explained below withreference to FIG. 10.

[0110] The image forming unit 21C has a known structure, which isillustrated in FIG. 10. The unit 21C includes a photoreceptor drum 25Cas an electrostatic latent image carrier, and also a charging unit 27C,a developing unit 26C, and a cleaning unit 28C that are disposed aroundthe drum 25C in this order along the rotational direction F of the drum25C. Further, writing light is received between the charging unit 27Cand the developing unit 26C. The image forming apparatus 20 in FIG. 9has the transferring unit 22 that is extended in a slanting direction,and therefore the transferring unit 22 occupies less space as comparedto the space occupied by the transferring unit 22 provided in ahorizontal direction.

[0111] The charging unit 27C includes, as shown in FIG. 10, of a rollerhaving the structure similar to that in FIG. 2. Abutting members thatprotrude towards the photoreceptor drum 25C are provided on both ends ofthe roller in the axial direction to set a prescribed gap between thephotoreceptor drum 25C and the roller of the charging unit 27C. Theprescribed gap is explained later.

[0112] The developing unit 26C uses a biaxial agitation method carriedout by agitating screws 26C1 and 26C2 which are two agitators that carryout mixing and agitating of toner supplied from a toner cartridge withmagnetic carrier. Developer is frictionally charged due to agitation andmagnetic carrier toner is adhered to the developer. The developer iscarried on a surface of a developing sleeve 26C3 as a developer carrier,and is provided with a magnetic roller that has north and south poleslined up inside. The developer is supplied toward the photoreceptor 25Cafter a layer thickness is regulated by a doctor blade 26C4.

[0113] The developing sleeve 26C3 in the developing unit 26C is disposedto set a prescribed gap from the photoreceptor drum 25C. In thestructure shown in FIG. 10, the prescribed gap is set to be less than orequal to 500 μm, preferably to 470 μm. This prescribed gap is set toallow the capability of toner adhesion to an electrostatic latent imageon the photoreceptor drum to be enhanced, the developing capability ofcontinuous black image to be improved, and uniform and identicaldevelopment with utmost clarity of fine lines such as characters anddots etc to be realized. It is possible to maintain uniform and highdeveloping capability of toner dots by giving identical reproducibilityto the electrostatic latent image by setting the gap less than or equalto 500 μm. Making the prescribed gap greater than 500 μm does notguarantee good capability.

[0114] The abutting members (not shown) provided on both ends of thedeveloping sleeve 26C3 in the axial direction are used for setting thegap between the developing sleeve 26C3 and the photoreceptor drum 25C.The abutting member is a member protruding toward the photoreceptor drum25C that is similar to the abutting member 105D in the charging unit 105shown in FIG. 2. In the embodiment, an abutting roller is used. Theprotruding roller is larger than the photoreceptor drum 25C and has anouter diameter equivalent to an amount of protruding more than theprescribed gap.

[0115] The structure in which the prescribed gap is set, enables tocarry out splashing of toner to an image area on the latent imagecarrier and returning of toner from non-image area to the developercarrier due to the bias characteristics according to the type ofdeveloper used in efficient manner. This can optimize the electricalfield effect by the bias and reliably prevent deterioration ofdeveloping capability and production of resonance in the latent imagecarrier.

[0116] The developing sleeve 26C3 maintains the gap of 470 μm from thephotoreceptor drum 25C and carries a developer that includes toner andcarrier made of the magnetic material. A negatively charged developingbias supplied from a power supply (not shown) is applied to thedeveloping sleeve 26C3. Negatively charged toner is splashed and appliedon an area of exposure of the photoreceptor drum 25C based on anelectric field created between the sleeve 16C3 and the drum 25C, therebycarrying out developing. Thus, a toner image is formed.

[0117] The developing bias to be used includes a first electricpotential area V1 and a second electric potential area V2 generated bysuperposing ac voltage on dc voltage as shown in FIG. 47. The firstelectric potential area V1 in which toner is moved from the developingsleeve 26C3 to the photoreceptor drum 25C, and the second electricpotential area V2 in which toner is moved from the photoreceptor drum25C to the developing sleeve 26C3. The negatively charged toner in thebrush-like developer on the surface of the developing sleeve 26C3 isadhered, due to an electrostatic force, to an area of electrostaticlatent image on the photoreceptor 25 by the developing bias.

[0118] At this time, an electrostatic force is produced so that apositively charged carrier is moved to an area of non-electrostaticlatent image on the photoreceptor 25. However, due to restraining ofcarrier by a magnetic force of a magnetic roll in a developing roller26C1, the positively charged carrier is not moved on to thephotoreceptor drum 25C. Using of such a type of developing bias improvescapability of toner deposition on the electrostatic latent image on thephotoreceptor drum 25C, improves developing capability of continuousblack image, and enables uniform developing with utmost clarity of finelines such as characters and dots etc. identical to the electrostaticlatent image.

[0119] In FIG. 10, a process cartridge is structured by supporting atleast one from among the charging unit 27C which sets the biascharacteristics to the photoreceptor drum 25C, the developing unit 26C,and the cleaning unit 28C having a cleaning blade 28C1 that is incontact with the photoreceptor drum 25C, by the same support as that ofthe photoreceptor drum 25C. The process cartridge is detachable from themain body of the image forming apparatus. Moreover, image forming unitsfor four colors can be collectively drawn out to an outer side.

[0120] The cleaning unit is provided not only for the photoreceptor drum25C. In addition, a cleaning unit 27C1 is provided for cleaning a rollerused in the charging unit 27C. The cleaning unit 27C1 eliminates foreignmatters like dust and toner reversely transferred from the photoreceptordrum 25C to the charging unit 27C, thereby preventing variation in theelectric field due to charging unevenness and carrying out stable anduniform charging.

[0121] On the other hand, the photoreceptor drum 25C is a cylinder of0.75 millimeter thick metal with a photosensitive layer provided on thesurface of the cylinder and a vibration absorber provided inside thecylinder.

[0122]FIG. 11 and FIG. 12 illustrate the internal structure of thephotoreceptor drum 25C. The vibration absorber (shown by referencenumeral 110′ and 110″ for convenience) that is formed by an elasticmaterial containing either of butyl rubber and nitrile rubber is fittedinside the photoreceptor drum 25C. The vibration absorber shown 110′ inFIG. 11 is in the form of a solid cylinder and the vibration absorber110″ shown in FIG. 12 is in the form of a hollow cylinder. It is notedthat the vibration absorber 110′ explained hereinafter includes thevibration absorber 110″ when the two absorbers do not need to beindividually explained. The vibration absorber 110′ is provided ineither of an area of the roller 102 in its axial direction where theroller tends to easily deform by bending and a region around this area.

[0123] The tangent of loss tan δ of the vibration absorber 110′ is setto be greater than or equal to 0.5 for the following reason. The tangentof loss tan δ means a tangent of phase angle δ (loss angle) of stressand strain in the material to be used in the vibration absorber, and thegreater the value of tan δ, the greater the damping effect is.

[0124] Following is a result of experiment carried out for measurementof the tangent of loss tan δ, and the measurement was carried outaccording to a non-resonant vibration method that is prescribed in theJapanese Industrial Standards (JIS) K7244-4. A sample having a thicknessof 2 millimeters, a width of 5 millimeters, and a length of 30millimeters was used as a specimen and a result was achieved by carryingout measurement at applying frequency of 30 Hertz. The solid cylinder asshown in FIG. 11 and the hollow cylinder as shown in FIG. 12 which havedifferent values of tangent of loss tan δ were prepared for samples forthe experiment.

[0125]FIG. 13 is graphical representation of results of the experiment.Acoustic power is on a vertical axis and the tangent of loss tan δ is ona horizontal axis in this figure. It is evident from the result of theexperiment that vibrations were reduced to a satisfactory level ofhearing (high frequency sound is not harsh to ears) when the value oftan δ is 0.5 or more in the solid cylindrical vibration absorber 110′ ofFIG. 11. Similarly, vibrations were reduced to a satisfactory level ofhearing when the value of tan δ is 0.6 or more in the hollow cylindricalvibration absorber 110″ of FIG. 12. Moreover, even stronger vibrationreduction effect can be achieved when the value of tan δ is 0.8 or more.Apart from noise due to the developing unit, noise due to the chargingunit and cleaning blades was also measured together during theexperiment.

[0126] From these results, practically satisfactory damping effect canbe achieved by setting the tangent of loss tan δ to 0.5 or more and evenbetter damping effect can be achieved when the value of tangent of losstan δ is set to 0.8 or more. Thus, resonance (noise) produced in thedeveloping unit 26, the charging unit 27, and the cleaning blade can bereduced. The structure of the vibration absorber 110′ in thephotoreceptor drum 25C is not limited to the photoreceptor drum 25C thatforms an image of cyan color only, but the same structure can be used inthe other photoreceptor drums as well.

[0127] The tangent of loss tan δ of the solid cylindrical vibrationabsorber 110′ of FIG. 11 is smaller than the tangent of loss tan δ ofthe hollow cylindrical vibration absorber 110″ of FIG. 12 because of thedifference in masses of the two vibration absorbers 110′ and 110″. Theharsh noise can be reduced effectively by changing the resonatingfrequency of the photoreceptor drum to the low frequency. The hollowcylinder is a favorable from the material cost point of view since thiscylinder uses less amount of material than the solid cylinder.

[0128] The vibration absorber 110′ is integrated into the photoreceptordrum 25C by either of press fitting and bonding. Assume that an innerdiameter of the photoreceptor drum is D and an outer diameter of thevibration absorber 110′ is d. If the vibration absorber 110′ is pressfitted and d is less than D, then damping effect and noise reductioneffect cannot be achieved because the vibration absorber is not fittedtightly to the inner surface of the photoreceptor. Conversely, if d isexcessively greater than D, excessive force is required for fixing thedamper inside the photoreceptor. This creates difficulties in assemblingand may result in deformation of the photoreceptor while assembling.Therefore, it is preferable that a relation between D and d is in arange of D≦d≦(D+1) mm.

[0129] Following is an explanation of the photoreceptor drum in whichthe vibration absorber 110′ is inserted. As a photoreceptor used inimage processing based on the electrophotographic method, one that usesan inorganic semiconductor material like selenium or amorphous silicon,etc., one that uses an organic semiconductor material, and one as acombination of the two are known. In recent years, the organicphotoconductors (photoreceptors) (OPC) have been used widely due totheir low cost, a high degree of flexibility in designing, andnon-polluting nature.

[0130] As the organic photoreceptor used in electrophotography, those asfollows are known photoreceptors. That is, the organic photoreceptorincludes a photoreceptor of photoconductive resins represented bypolyvinyl carbazole (PVK), a charge transfer complex type photoreceptorrepresented by PVK-TNF (2,4,7-trinitrofluorenone), a pigment dispersingtype photoreceptor represented by phthalocyanine binder, and a functionseparated type photoreceptor used as a combination of charge generatingmaterial and charge carrying material. Especially, the functionseparated type photoreceptors have been focused on. The mechanism in theelectrostatic latent image forming in the function separated typephotoreceptors is as follows. When light is irradiated after thephotoreceptor is charged, the light passes through a transparent chargecarrying layer, and is absorbed by the charge generating material in thecharge generating layer. The charge generating material that hasabsorbed the light generates charge carriers and these charge carriersare injected into the charge carrying layer. The charge carriers moveinside the charge carrying layer according to an electric fieldgenerated by charging and an electrostatic latent image is formed due toneutralization of charge on the surface of the photoreceptor.

[0131] In the function separated type photoreceptors, it is known anduseful to use a combination of the charge carrying material that absorbslight mainly in an ultraviolet region with the charge generatingmaterial that absorbs light mainly in a visible region.

[0132] However, the organic-based electrophotographic photoreceptorshave poor mechanical and chemical durability, which is a knownshortcoming. Most of the charge carrying materials is developed as lowmolecular compounds. However, the low molecular compounds do not have acapacity to form a membrane independently. Therefore, the compounds aredispersed into or mixed with inactive high molecules to be used.Generally, the charge carrying layer, including the low molecular chargecarrying material and inactive high molecules, is soft and has poormechanical durability. In the electrophotography process, mechanicalload exerted by various parts coming in contact (developing unit,charging unit, transfer paper, cleaning brush, cleaning blade etc.)tends to break the membrane easily.

[0133] Therefore, a protective layer that contains filler to protect aphotosensitive layer and to improve the durability of the photosensitivelayer is also provided on the photosensitive layer as a top layer. Amaterial used for the protective layer includes resins such as ABSresin, ACS resin, olefin vinyl monomer copolymer, chlorinated polyetherresin, allyl resin, phenolic resin, polyacetal resin, polyamide resin,polyamide imide resin, polyacrylate resin, polyallyl sulfone resin,polybutylene resin, polybutylene terephthalate resin, polycarbonateresin, polyether sulfone resin, polyethine resin, polyetheleneterephthalate resin, polyimide resin, acrylic resin, polymethale pentaneresin, polypropylene resin, polyphenylene oxide resin, polysulfoneresin, AS resin, AB resin, BS resin, polyurethane resin, polyvinylchloride resin, polyvinyledene chloride resin, and epoxy resin. A fillerto be added to further improve the wear resistance of the protectivelayer includes fluororesin like polytetra fluoroethylene, and siliconresin, and these resins dispersed with inorganic materials like titaniumoxide, tin oxide, potassium titanate, silica, alumina, etc.

[0134] Quantity of the filler to be added to the protective layer byweight is normally in a range of 10% to 40%, preferably in a range of20% to 30%. When the quantity of the filler is less than 10%, the wearis increased, which deteriorates the durability. When the quantity ofthe filler is more than 40%, rise in electric potential in a bright areaduring exposure is increased and photographic sensitivity drops to theextent that cannot be neglected, hence more than 40% is not desirable.Moreover, dispersion-assisting agent can be added to the protectivelayer to improve dispersion of the filler. A dispersion-assisting agentused in paints can be used for adding. Normally, the quantity of thedispersion-assisting agent with respect to the quantity of the fillercontained is in a range of 0.5% to 4%, preferably in a range of 1% to2%. Furthermore, adding of charge carrying material to the protectivelayer is also effective and an antioxidant can also be added ifnecessary. A method of forming the protective layer includes a normalcoating method like a spraying method.

[0135] The thickness of the protective layer is in a range of 0.5 μm to10 μm, preferably in a range of about 41 μm to 6 μm. An intermediatelayer can be provided between the photosensitive layer and theprotective layer of the photoreceptor used in the embodiment. Normally,a binder resin is used as a main component in the intermediate layer.The resins for the binder or the like include polyamide, alcohol-solublenylon, water-soluble polyvinyl butyral, polyvinyl buteral, or polyvinylalcohol. A method of forming the intermediate layer includes the normalcoating method. The appropriate thickness of the intermediate layer isin a range of about 0.05 μm to 2 μm.

[0136] The inventors of the present invention carried out an experimenton the noise reduction effect when the vibration absorber was fittedinside the photoreceptor having the above structure, and the followingresult was obtained. Following is an explanation about the photoreceptorthat is used in this experiment.

[0137] A photoreceptor for evaluation is similar to the one explained inthe previous embodiment that employs a hollow cylinder having an outerdiameter of 30 millimeters, an inner diameter of 28.5 millimeters, and awall thickness of 0.75 millimeter.

[0138] (1) Making of Photoreceptor (No. 1) for Evaluation

[0139] Solutions of compositions given below were sequentially coated onan aluminum drum having an outer diameter φ 30 millimeters and dried.The solutions include a coating solution for undercoat layer, a coatingsolution for charge generating layer, and a coating solution for chargecarrying layer. When the coated layers were dried, the undercoat layerof thickness 3.5 μm, the charge generating layer of thickness 0.2 μm,and the charge carrying layer of thickness 25 μm were formed. Thus,electrophotographic photoreceptor (photoreceptor No. 1) for evaluationwas obtained.

[0140] Coating Solution for Undercoat Layer:

[0141] Alkyd resin: 6 weight parts (Bekkozol 1307-60-EL made byDAINIPPON INK & CHEMICALS INDUSTRIES)

[0142] Melamine resin: 4 weight parts (Super Bekkamine G-821-60 made byDAINIPPON INK & CHEMICALS INDUSTRIES)

[0143] Titanium oxide: 40 weight parts

[0144] Methyl ethyl ketone: 200 weight parts

[0145] Coating Solution for Charge Generating Layer:

[0146] Trisazo pigments with the formulation as shown in chemicalformula 1: 2.5 weight parts

[0147] Polyvinyl butyral (UCC: XYHL): 0.25 weight parts

[0148] cyclohexanone: 200 weight parts

[0149] methyl ethyl ketone: 80 weight parts

[0150] Coating Solution for Charge Carrying Layer:

[0151] Bisphenol A-type polycarbonate: 10 weight parts (Panlite K1300made by TEIJIN)

[0152] Low molecular charge carrying material with the formulation asshown in chemical formula 2: 10 weight parts

[0153] Methylene chloride: 100 weight parts

[0154] (2) Making of Photoreceptor (No. 2) for Evaluation

[0155] The photoreceptor (No. 2) for evaluation was made by forming aprotective layer with a thickness of 2 μm on the charge carrying layerof the photoreceptor (No. 1) using a coating solution for protectivelayer with the formulation given below. The remaining layers of thephotoreceptor (No. 2) were the same as in the photoreceptor (No. 1).

[0156] Coating Solution for Protective Layer:

[0157] Charge carrying material with the formulation as shown inchemical formula 3: 2 weight parts

[0158] A-type polycarbonate: 4 weight parts

[0159] Methylene chloride: 100 weight parts

[0160] (3) Making of Photoreceptor (No. 3) for Evaluation

[0161] The photoreceptor (No. 3) for evaluation was made by forming aprotective layer with a thickness of 2 μm on the charge carrying layerof the photoreceptor (No. 1) using a coating solution for protectivelayer with the formulation shown in chemical formula 3. The remaininglayers of the photoreceptor (No. 3) were the same as in thephotoreceptor (No. 1).

[0162] Coating Solution for Protective Layer:

[0163] Charge carrying material with the formulation as shown inchemical formula 3: 4 weight parts

[0164] A-type polycarbonate: 4 weight parts

[0165] Titanium oxide: 1 weight part

[0166] Methylene chloride: 100 weight parts

[0167] (4) Making of Photoreceptor (No. 4) for Evaluation.

[0168] The photoreceptor (No. 4) for evaluation was made by substitutingtitanium oxide for a filler which was dispersed in the protective layerof the photoreceptor (No. 3), by aluminum oxide. The remaining layers ofthe photoreceptor (No. 4) were the same as in the photoreceptor (No. 3).

[0169] The inventors of the present invention achieved following resultsby carrying out experiments using the photoreceptors for evaluation No.1 to No. 4. The experiments were carried out on quality of images oneach of the photoreceptors and on noise caused by the case where thevibration absorber was fitted in the photoreceptor.

[0170] In the experiments, a continuous paper-feeding test was carriedout with a digital copying machine IMAGIO MF 200 (trade name) made byRICOH COMPANY, LTD. The image quality (overall evaluation of imagedensity, resolution etc.) was found to be very good. A F-to-C ratiobetween molecules of fluorine and carbon on the surface of thephotoreceptor as an index for deposition of fluorine-based materialexisting on the surface of the photoreceptor was found to be zero.Moreover, during running of the copying machine, the amount of decreaseAd from an initial value in the thickness of the photosensitive layerwas found to be appropriate and hard copies having high definition couldbe obtained with stability during long period of time.

[0171] In the photoreceptors No. 1 to No. 4, the vibration absorber 110′was fitted as shown in FIG. 11 and FIG. 12 and developing bias in whichac voltage was superimposed on dc voltage was applied to thephotoreceptors. As a result, resonance in the photoreceptors wasreduced, transmission of vibrations of a cleaning blade was prevented,and prevention of noise generation was confirmed.

[0172] Following is an explanation of practical application of thepresent invention.

[0173]FIG. 14 illustrates a laser printer as an example of the imageforming apparatus that uses a one-component developer using magnetictoner as a developer. In a case of using the one component developer,structure of a basic image forming section resembles to that of an imageforming apparatus that uses a two-component developer.

[0174] In FIG. 14, reference numeral 50 is an image carrier in the formof a drum (hereinafter “photoreceptor drum”) provided inside the mainbody of the printer. Right side of the figure is a front side of theprinter. When the printer is in use, the photoreceptor drum 50 rotatesin a direction of an arrow shown in the figure (in counterclockwisedirection). To start with, a charging roller 51 charges the surface ofthe photoreceptor drum 50 uniformly and then writing is carried out byirradiating laser light L from an optical writing unit thereby formingan electrostatic latent image on the surface of the photoreceptor drum50.

[0175] A developing unit 52 provided adjacent to the photoreceptor drum50 includes a developing roller 53. A prescribed gap between thephotoreceptor drum 50 and the developing roller 53 is set to 300 μm orless, preferably 280 μm. The one-component developer stored in adeveloper storage 68 is carried on the surface of the developing roller53 and is supplied to the photoreceptor drum. The prescribed gap is setto prevent deterioration of developing capability when dc voltage isapplied and further ac voltage is applied in addition, similar to thecase of using the two-component developer. When this gap is excessivelylarge and the developing roller 53 is farther away from thephotoreceptor drum 50, the improvement in the developing capacity whenthe ac voltage image is superimposed on the dc voltage, is affected.When the gap is set to be less than 300 μm i.e. to be made narrow, it ispossible to further improve the high developing capacity such that adeveloped image is identical to a latent image having utmost clarity andtoner dots are uniform. To maintain this prescribed gap, an abuttingroller is used like in the case of the developing sleeve 26C3 as shownin FIG. 10.

[0176] To adhere magnetic toner as the one-component developer to thephotoreceptor drum 50, a developing bias having dc voltage superimposedby ac voltage on it by a power source not shown is applied to thedeveloping roller 53 in addition to an electrostatic absorption force ofan electrostatic latent image formed on the surface of the photoreceptordrum 50 are applied combined on the developing roller 53. The magnetictoner is supplied to the photoreceptor drum 50 by the developing roller53 in the developing unit 52 through rotation of the photoreceptor drum50 to develop an electrostatic latent image on the photoreceptor drum50.

[0177] The developing unit 52 includes known components such as adeveloping blade 54 that scrapes the developing roller 53 therebycarrying out frictional charging to toner, an agitating shaft 55 and anagitator 56 that agitate and carry the toner, and a toner ending sensor57 that detects the quantity of the toner remaining in the developingunit.

[0178] In the structure shown in FIG. 14, a vibration absorber isincluded in the photoreceptor drum 50 similarly as shown in FIG. 10. Forthe structure, the structures shown in FIG. 11 and FIG. 12 are used.

[0179] In FIG. 14, a sheet-like recording material which is stored in apaper-feeding cassette (not shown) is fed along the rotation of thephotoreceptor drum 50, and the recording material stops for a time whenit is held between a pair of register rollers 59. When the pair ofregister rollers 59 rotates with the timing matched with that of animage on the photoreceptor drum 50, the recording material is guided bya part 70A on an outer surface of a cartridge case 70 and forwarded to atransfer nip between the photoreceptor drum 50 and the transfer roller60. A toner image on the photoreceptor drum 50 is transferred to therecording material through a transfer bias from the transfer roller 60.

[0180] After transferring of the image to the recording material, therecording material is decharged by a decharging pin 61 and carriedupward through a carrier path in a state of the material as indicated bya reference numeral S. The recording material is then guided to a fixingnip formed at a position where a pressure roller and a fixing roller ofthe fixing unit not shown are in contact with each other. Here, thetransferred image is fixed by heat and pressure, and the recordingmaterial is discharged to a paper discharging section with an imagesurface facing downward.

[0181] Residual toner on the photoreceptor drum 50 after havingtransferred the image is eliminated by a cleaning blade 58 of thecleaning unit 57 through the rotation of the photoreceptor drum 50. Thephotoreceptor drum 50 is kept ready for recharging by the chargingroller 51.

[0182] In the laser printer structured as shown in FIG. 14, thephotoreceptor drum 50, the charging roller 51, the developing unit 52,and the cleaning unit 57 etc., are accommodated in the cartridge case 70as a casing of the printer, thereby forming a process cartridge 71. Themain body of the image forming apparatus is made compact in size byimproving an accuracy of relative position of each component withrespect to the other component. The handling is made easier by enablingthe replacement of parts at a time instead of replacing them atdifferent times. The maintenance of the image forming apparatus is madesimple to make its life longer.

[0183] Thus, according to the first embodiment, the vibration absorberis disposed on the side opposite to the surface facing the unit in whichthe bias characteristics are set in the latent image carrier. Therefore,due to the bias characteristics, the vibration absorber that is incontact with the latent image carrier absorbs a part of the vibrationsin the latent image carrier, which is caused by the vibrating electricfield generated when ac voltage is applied. This enables to reduce theresonance of the latent image carrier, thereby preventing noise. Even ifthe latent image carrier is either of a belt and a thin-walled cylinder,noise can be prevented without increasing the mass and complicating thestructure of the latent image carrier.

[0184] Further, since the vibration absorber is in the form of a rollerand the strong vibration absorbing material is provided either on thesurface of the absorber or inside the absorber, the propagation ofvibrations is prevented when the roller is in contact with the latentimage carrier. Thus, the noise due to resonance in the latent imagecarrier is prevented.

[0185] Moreover, since the drive roller is used as the vibrationabsorber when the latent image carrier is in the form of a belt, amaterial that comes in firm contact with the latent image carrier, canbe used as a damper. This facilitates the absorption of vibrationsgenerated in the latent image carrier and enables to reduce theresonance in the latent image carrier by using the existing structure.

[0186] When the latent image carrier is a belt, the vibration absorberis provided on the opposite side of the surface of the supporting platewhere the supporting plate is in contact with the latent image carrier.The supporting plate is made of a rigid body in the form of a flat platethat is in contact with the belt. Therefore, the vibration absorberabsorbs the vibrations generated in the belt without obstructing themovement, and resonance produced in the latent image carrier can bereduced.

[0187] Since the vibration absorber is disposed in a position oppositeto the unit in which the bias characteristics with respect to the latentimage carrier are set, the resonance can be reduced in the mosteffective manner at the origin of resonance produced in the latent imagecarrier due to the bias characteristics.

[0188] Since the latent image carrier is a substrate in the form of athin belt made of a material that absorbs strong vibrations, thematerial can reduce the vibrations of the latent image carrier ascompared to the case where a photosensitive layer is provided on thesurface of the thin belt-like substrate. Therefore, there is no need tohave a special arrangement for damping and hence no extra cost isneeded.

[0189] By setting the value of tangent of loss tan δ which affects thedamping effect to a value greater than or equal to 0.5, the frequency ofresonance can be varied to the frequency range in which high frequencysound that is harsh to ears is not generated. Therefore, even when thenoise is generated from the latent image carrier, the same effect asthat of reducing the noise can be achieved.

[0190] Since the vibration absorber is in the solid cylindrical form, itis possible to vary the resonance frequency of the latent image carrierto the low frequency range efficiently by using the difference of masscompared to that of the hollow cylindrical form. Thus, the resonancecaused by the vibrations of the latent image carrier can be preventedand noise can be reduced in an efficient manner.

[0191] It is possible to reduce the material cost by using the vibrationabsorber in the hollow cylindrical form. In a case of the structure thatleads to the reduction in the material cost, in other words, even in acase where it is difficult to decrease the resonance frequency due tothe mass different from that in a case of the solid cylindrical form,deterioration of the damping effect can be prevented reliably by settingthe value of tangent of loss tan δ which affects the damping effect to avalue greater than or equal to 0.6.

[0192] Moreover, since the vibration absorber is fitted inside thelatent image carrier by either of press fitting and bonding, it isthoroughly integrated with the latent image carrier thereby reducing theresonance in the latent image carrier in an efficient manner.

[0193] A second embodiment of this invention will be explained below.

[0194]FIG. 15 is a cross section of a schematic structure of an imageforming apparatus that uses an image carrier drum in the form of ahollow cylinder according to the second embodiment. An image carrierdrum 202 in the figure is a photoreceptor drum with a photosensitivelayer provided on an outer peripheral surface of a circular cylindricaltube made of a conductive metal like aluminum. In an example shown inFIG. 15, an image forming module 218 is structured by assembling theimage carrier drum 202 integrally with an image forming unit that formsa toner image as explained later. The image carrier drum 202 isrotatably supported by a case 219 of the image forming module 218, andis driven by a drive motor (not shown) in the clockwise direction inFIG. 15. At this time, a charging roller 220 as an example of a chargingunit rotatably supported by the case 219 is rotated, and a chargingvoltage is applied to the charging roller 220. Thereby, the surface ofthe image carrier drum 202 is charged to a prescribed polarity. In thisimage forming apparatus, a spacer including a tape 201 is wound aroundeach end of the charging roller 220 in its longitudinal direction. Thetape 201 is in contact with the outer peripheral surface of the imagecarrier drum 202 and the charging roller 220 is in a position such thatthere is a minute gap with respect to the surface of the image carrierdrum 202.

[0195] A modulated laser beam L emitted from an exposing unit (notshown) is irradiated on the surface of the image carrier drum aftercharging, and an electrostatic latent image is formed on the imagecarrier drum. It is noted that the exposing unit is provided separatelyapart from the image forming module 218. This electrostatic latent imageis visualized as a toner image by a developing unit 222. The toner imageis carried on a transfer belt 208 and is transferred to a recordingmedium P like a transfer paper etc. that travels in a direction of anarrow A by an action of a transfer brush 209. The transfer brush 209 isan example of a transferring unit. When the toner image having beentransferred to the recording medium P passes through a fixing unit (notshown), the toner image is fixed on the recording medium P due to effectof heat and pressure. A residual toner on the image carrier drum that isleft after the transferring of the toner image is eliminated by combinedaction of a cleaning brush 229 and a cleaning blade 230 of a cleaningunit 227.

[0196] The developing unit 222 includes a developing case 223 formedwith a part of the case 219 of the image forming module 218, and adeveloping roller 224 rotatably supported by the developing case 223.The developing case 223 contains developer D. The rotating developingroller 224 carries the developer D and transfers it. The transferreddeveloper visualizes the electrostatic latent image. In this case, thetwo-component developer including toner and carrier, is used. When adecrease in toner density of the developer is detected, the developingcase 223 is replenished with the toner from a toner container 233. Thecleaning unit 227 includes a cleaning case 228 also formed with a partof the case 219 of the image forming module 218. The cleaning brush 229and the cleaning blade 230 are supported by the cleaning case 228. Thus,in the image forming apparatus shown in FIG. 15, the image carrier drum202 and the image forming units, arranged around the drum, such as thecharging roller 220, the developing roller 224, the cleaning brush 229,and the cleaning blade 230 are integrally assembled to the case 219 toform the image forming module 218. The image forming module 218 isdetachable from the casing (not shown) of the image forming apparatusand can be replaced by a new image forming module when the modulereaches end of its life.

[0197] Thus, in the image forming apparatus, the toner image is formedon the surface of the rotating image carrier drum 202, and the formedtoner image is then transferred to the recording medium P to achieve arecorded image. The fixing unit fixes the toner image that has beentransferred on the recording medium P. The toner having a low meltingpoint is used in the developing unit to enable the fixing of the tonerimage in the fixing unit at a comparatively low surface temperature of afixing roller, for example, 145° C. The image forming apparatus forms atoner image on the image carrier drum using toner having an outflowstart temperature, measured by flow tester method, of less than or equalto 102° C., preferably in a range of 99° C. to 102° C. A Shimadzu FlowTester CFT500 made by SHIMADZU SEISAKUSHO is used for measurement of theoutflow start temperature by the flow tester method.

[0198] This flow tester is provided to melt a test sample in a cylinderby heating the cylinder from outside, apply pressure with a constantload by a piston from the topside of the cylinder, and extrude the testsample through pores in a die disposed at a bottom of the cylinder. Atemperature at which the melted test sample starts extruding from thepores of the die is an outflow start temperature. By using toner havingan outflow start temperature less than or equal to 102° C., the tonerimage is formed on the image carrier drum. Specifically, the toner isused under setting conditions as follows, load exerted on the piston: 10kg/cm², temperature rising rate: 3.0° C./min, diameter of pore in thedie: 0.5 millimeter, and die length: 10 millimeters. The flow testermethod is described in Japanese Patent Application Laid OpenPublications No. 2001-147551 and No. 2001-75106.

[0199] The charging roller 220 is disposed on the outer peripheralsurface of the image carrier drum 202 in FIG. 15 and the cleaning blade230 is in contact with the surface of the drum. When charging voltagehaving ac voltage superimposed on dc voltage is applied to the chargingroller 220, the charging roller 220 vibrates due to the application ofthe ac voltage. Further, the cleaning blade 230 vibrates due tostick-slip during rotation of the image carrier drum 202. Thesevibrations transmitted to the image carrier drum 202 may cause the drum202 to vibrate and lead to generation of noise. Especially, when thetoner having a low melting point is used, a large amount of noise may begenerated in the conventional image forming apparatus thereby causingthe user to feel uncomfortable. As a tube of the image carrier drum 202,a thin-walled hollow cylinder made of aluminum is used. This tube has anouter diameter of about 30 millimeters, an inner diameter of about 28.5millimeters, and a wall thickness of about 0.75 millimeter. Theconventional image forming apparatus tends to generate noise easily whenthe image carrier drum 202 formed of such a thin tube is used.

[0200] Therefore, a damper 204 is provided inside the image carrier drum202 in the image forming apparatus as shown in FIG. 15 and FIG. 16. Thedamper 204 shown in FIG. 17 can also be used. The damper 204 is formedof a material having a tangent of loss tan δ greater than or equal to0.5. The tangent of loss tan δ is a tangent of a phase angle δ (lossangle) of stress and strain in the material. The greater the value oftangent of loss tan δ, the greater the damping effect is.

[0201] In the image forming apparatus, considering the characteristicsof this type of damping material, the damper 204 made of the materialhaving a tangent of loss tan δ greater than or equal to 0.5 is providedto effectively suppress vibrations of the rotating image carrier drum202. Even by using the toner having a low melting point, it is possibleto reduce the noise generated in the image carrier drum 202 during imageformation to an extremely low level. A rubber material like butylrubber, nitrile rubber etc. can be used as a material having the tangentof loss tan δ greater than or equal to 0.5.

[0202] The inventors of the present invention provided the damper 204made of rubber as shown in FIG. 17 having a value of the tangent of losstan δ0.5 and the damper 204 made of ABS resin having a value of thetangent of loss tan δ less than 0.5 inside the image carrier drum 202respectively as shown in FIG. 15, and carried out image forming to findout if the noise was audible to a person who was present in the vicinityof the image forming apparatus. The charging voltage in which an acvoltage was superimposed on dc voltage was applied on the chargingroller 220. The inventors used two types of toner. One of the toners hadan outflow start temperature of 102° C. or less and had a low meltingpoint such that the toner image could be fixed at a surface temperatureof the fixing roller of about 145° C. in the experimental apparatus. Theother toner had the outflow start temperature of higher than 102° C. anda high melting point such that the toner image could be fixed at asurface temperature of the fixing roller of about 175° C. The tangent ofloss tan δ of the damper 204 was measured according to a non-resonantvibration method prescribed in JIS K7244-4. A specimen having athickness of 2 millimeters, a width of 5 millimeters, and a length of 30millimeters was used, and measurement was carried out at appliedfrequency of 30 Hertz. The results of the experiment are shown intable 1. TABLE 1 Toner having a high Toner having a low melting pointmelting point Damper made of ABS No generation of Generation of noiseresin noise Damper made of No generation of No generation of noiserubber having tan δ 0.5 noise

[0203] In table 1, “generation of noise” means that the person observingthe experiment being in the vicinity of the image forming apparatuscould clearly hear the noise, and “no generation of noise” means thatthe noise was not heard. As can be seen in table 1, even with the tonerhaving the low melting point, when the damper 204 made of a materialthat had the tangent of loss tan δ0.5 was inserted inside the imagecarrier drum 202, generation of noise was not noticed. With the sametoner, when the damper 204 made of a material that had the tangent ofloss tan δ less than 0.5, generation of noise was confirmed. When thesame experiment was carried out without inserting the damper inside theimage carrier drum, significant noise generation was recognized by usingeither of the toners.

[0204] When the damper 204 is formed of a material that has the tangentof loss tan δ greater than 0.5, particularly 0.6 or more, or even 0.8 ormore, the damping effect to the image carrier drum 202 can be improvedconsiderably.

[0205] When a toner including a metallic salt of high fatty acid like azinc stearate is used as a toner for the image forming apparatus, a partof the toner gets deposited on the surface of the image carrier drum202. Due to the toner deposited on the surface, the coefficient offriction of the toner with the cleaning blade decreases therebyimproving slip of an edge of the cleaning blade 230. This reducesvibrations in the cleaning blade and further improves the effect ofpreventing noise generation.

[0206] The damper 204 in FIG. 16 is in a solid circular cylindrical formwhereas the damper 204 in FIG. 17 is in a hollow circular cylindricalform. When the solid damper 204 as shown in FIG. 16 is used, the weightof the damper 204 is increased, and thereby the overall weight of theassembly of the damper 204 and the image carrier drum 202 increases.Thus, high frequency noise that is harsh to ears can be reducedeffectively. On the other hand, when the hollow damper 204 as shown inFIG. 17 is used, the material used for the damper can be reduced and thecost can be also reduced. In such a case, the tangent of loss tan δ, theweight, the form, especially the thickness of the damper 204 has to beset appropriately to obtain required damping effect. It is possible touse the damper 204 molded in a hollow circular cylindrical form, and itis also possible to structure the damper 204 in the hollow circularcylindrical form by rolling up the sheet-like material. According to thelatter method, the damper 204 in the hollow circular cylindrical formcan be fabricated at a low cost using the sheet-like material therebyreducing the cost considerably.

[0207] As a method of fixing the damper 204 into the image carrier drum202, methods as follows can be employed. One of the methods is realizedby inserting, by press fitting, a damper into the image carrier drum202. More specifically, the damper has a setting such that d is slightlylarger than D where d is an outer diameter of the damper 204 beforebeing inserted into the image carrier drum 202 and D is an innerdiameter of the image carrier drum 202. Another method is realized bysetting d to be slightly smaller than D, inserting such a damper 204into the image carrier drum 202, and fixing the damper 204 to the innerwall surface of the image carrier drum 202 with an adhesive. Sufficientdamping effect can be achieved by using either of the methods. However,in the case of press fitting the damper inside the image carrier drum,if d is smaller than D, then the damper 204 is not fitted tightlyagainst the inner wall surface of the image carrier drum 202 therebydeteriorating the damping effect. Conversely, if d is excessively largerthan D, excessive force is required for inserting the damper 204 intothe image carrier drum 202. This not only creates difficulties inassembling but also results in deformation of the image carrier drumduring assembling. Therefore, it is preferable to have a relationbetween values of D and d such that D≦d≦(D+1) millimeter.

[0208] When the damper is fixed inside the image carrier drum by pressfitting, there is no need to use an adhesive and the cost for thisfixing can be reduced. Besides, the damper 204 can be removed from theimage carrier drum 202 easily and can be recycled. Whereas, when thedamper 204 is fixed inside the image carrier drum 202 by using theadhesive, it can be fixed very firmly.

[0209] The image forming apparatus in FIG. 15 has the cleaning blade 230that is in press contact with the surface of the image carrier drum 202to clean the surface thereof after transferring of the toner image. Itis possible to eliminate foreign matters like paper dust etc. that arecaught between the cleaning blade 230 and the surface of the imagecarrier drum 202 by rotating the image carrier drum in the reversedirection by only a small angle when the image carrier drum is stopped.A mode for a reverse direction of rotation is set. In this mode, theimage carrier drum 202 is rotated in a reverse direction to a rotatingdirection i.e. a forward direction of the image carrier drum 202 duringformation of the toner image on the drum. However, when the mode is set,the noise that originates from the vibrations of the cleaning blade 230may be generated not only during the rotation of the drum in the forwarddirection but also during the rotation of the drum in the reversedirection. In the conventional image forming apparatus, noise tends tobe generated particularly just before the image carrier drum 202 stopsits rotation, and when the image carrier drum 202 performs operations offorward rotation, stop, reverse rotation, and stop, a loud noise isgenerated twice consecutively. However, by providing the damper 204having the structure, inside the image carrier drum 202, it is possibleto prevent generation of loud noise even during reverse rotation of theimage carrier drum 202.

[0210] Following is the explanation of the image carrier drum 202 inwhich the damper 204 is fitted. As a photosensitive layer of the imagecarrier drum used in electrophotography, those as follows are known.That is, the photosensitive layer includes a photosensitive layer usingan inorganic semiconductor material such as selenium and amorphoussilicon, a photosensitive layer using an organic semiconductor material,and a photosensitive layer using a combination of the two. In recentyears, the organic photosensitive layer has been used widely due to itslow cost, a high degree of flexibility in photoreceptor designing, andnon-polluting nature. The damper mentioned above can be fitted in theimage carrier drum having either of the photosensitive layers.

[0211] As the organic photosensitive layer used in electrophotography,those as follows are known. That is, the organic photosensitive layerincludes a photosensitive layer of photoconductive resins represented bypolyvinyl carbazole (PVK), a charge transfer complex type photosensitivelayer represented by PVK-TNF (2,4,7-trinitrofluorenone), a pigmentdispersing type photosensitive layer represented by phthalocyaninebinder, and a function separated type photosensitive layer used as acombination of charge generating material with charge carrying material.Especially, the function separated type photosensitive layer has beenfocused on. The mechanism of forming the electrostatic latent image inthe function separated type photosensitive layer is as follows. That is,when light is irradiated after charging of the photosensitive layer, thelight passes through a transparent charge carrying layer and is thenabsorbed by the charge generating material in the charge generatinglayer. The charge generating material that has absorbed the lightgenerates charge carrier, and the charge carrier is injected in thecharge carrying layer to move in the charge carrying layer according toan electric field created by charging. Then, an electrostatic latentimage is formed due to neutralization of charges on the surface of thephotosensitive layer. In the function separated type photosensitivelayer, it is known and useful to use a combination of the chargecarrying material that absorbs light mainly in the ultraviolet regionwith the charge generating material that absorbs light mainly in thevisible region.

[0212] However, the organic photosensitive layer has poor mechanical andchemical durability, which is a known shortcoming. Most of the chargecarrying materials is developed as low molecular compounds. However,since the low molecular compounds do not have a capacity to form amembrane independently, the compounds are used after being dispersed inand mixed with inactive high molecules. Generally, the charge carryinglayer, formed of the low molecular charge carrying material and inactivehigh molecules, is soft and has poor mechanical durability. In theelectrophotography process, mechanical load exerted by various partscoming in contact (developing, transfer paper, cleaning brush, andcleaning blade etc.) tends to break the layer easily due to repetitiveuse of the layer.

[0213] Therefore, the protective layer can be provided on thephotoreceiving layer as a top layer made of these materials to protectthe photosensitive layer and to improve the durability thereof. Asexplained above, adding of charge carrying materials to the protectivelayer is also effective, and an antioxidant can also be added ifnecessary.

[0214] Moreover, an intermediate layer can be provided between thephotosensitive layer and the protective layer. Normally, a binder resinis used as a main component in the intermediate layer. Polyamide,alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinylbuteral, polyvinyl alcohol etc. are examples of the binder resin. Theintermediate layer is formed by the normal coating method. Theappropriate thickness of the intermediate layer is in a range ofapproximately 0.05 μm to 2 μm.

[0215] When the image carrier drum has the protective layer on itssurface, the breaking of the photosensitive layer is suppressed. Due tothis, the cleaning blade can be pressed against the image carrier drumwith even stronger force. Therefore, it is possible to clean wax etc. inthe toner that gets deposited on the image carrier drum when the tonerhaving a low melting point is used. Moreover, the variation in thefriction coefficient of the surface of the image carrier drum isreduced. That is, it is possible to have better cleaning and betternoise prevention.

[0216] When filler is included in the protective layer, the breaking ofthe photosensitive layer can be suppressed reliably thereby furtherimproving the effect of the protective layer.

[0217] When the charge carrying material is included in thephotoelectric layer, the breaking of the photosensitive layer can besuppressed reliably thereby further improving the effect of theprotective layer.

[0218] In the image forming apparatus in FIG. 15, the image formingmodule 218 is structured by integrally assembling the image carrier drum202 and a plurality of image forming units used for forming the tonerimage on the drum 202. However, the image forming module 218 can bestructured by integrally assembling at least the drum 202 and thecleaning blade 230 that cleans the surface of the drum 202 aftertransferring of the toner image. In such a case, values of resilienceand Young's modulus etc. vary due to temperature and humidity of an areaaround the cleaning blade 230. When the temperature and humidityincrease, the cleaning blade tends to vibrate easily and the imagecarrier drum tends to generate noise easily.

[0219] Therefore, it is useful to provide an environmental control unitto maintain at least either one of the temperature and the pressure ofthe image forming module at a predetermined value or below. Concretely,a sensor 203 that detects either of temperature and humidity or both isprovided in the image forming module 218 as shown in FIG. 15. When thesensor 203 detects that either of temperature and pressure or bothinside the image forming module 218 is a predetermined value or more, afan (not shown) provided in the casing of the image forming apparatusstarts. The fan blows air inside the image forming module 218 in thedirection indicated by arrows E and cools down the cleaning blade 203.This reduces the generation of noise more effectively.

[0220] In the image forming apparatus shown in FIG. 15, the chargingunit is formed with the charging roller 220 that is disposed close tothe image carrier drum 202. The image carrier drum 202 with the damperinserted into it, can also be used in an image forming apparatus thatuses any other type of charging units as shown in FIG. 18 to FIG. 20.Each of the charging units shown in FIG. 18 to FIG. 20 is a contact typecharging unit that is in contact with the surface of the image carrierdrum 202 formed with a photoreceptor drum that rotates in a direction ofan arrow to charge the image carrier drum 202. Each of the chargingunits is formed with a charging roller 220A, a brush roller 220B, or amagnetic brush unit 220C.

[0221] The charging roller 220A shown in FIG. 18 is formed with a coremetal 237 a and a conductive rubber layer 237 b fixed on its outerperipheral surface. Two ends of the core metal 237 a are supported bybearings (not shown) such that the core metal can rotate freely. Thecharging roller 220A is pressed against the image carrier drum 202 by apressurizing unit (not shown) with prescribed pressure and rotatesfollowing the rotation of the image carrier drum 202. Concretely, therubber layer 237 b having medium resistance of about 1×10⁵ ohm-cm coversthe core metal 237 a having a diameter of 9 millimeters. A diameter ofthe charging roller 220A is 16 millimeters. The core metal 237 a isconnected to a power source 250, which applies a prescribed bias to thecharging roller 220A. Due to application of the bias, the outer surfaceof the image carrier drum 202 is charged uniformly to a prescribedpolarity and electric potential. The damper is fitted inside the imagecarrier drum 202. Due to the effect of the damper, the generation ofnoise in the image carrier drum is reduced even when the chargingvoltage in which ac voltage is superimposed on dc voltage is applied tothe charging roller 220A.

[0222] In an example shown in FIG. 19, a brush 247 b of the brush roller220B is in contact with the surface of the image carrier drum 202 with aprescribed pressure so as to have a prescribed nip. The brush is made ofany of carbon, copper sulfide, metal, and metallic oxides, and issubjected to conductivity processing. The brush is wound or stuck arounda metal or any other core metal subjected to conductivity processing toform the charging roller (brush roller) 220B.

[0223] More specifically, a tape in which a conductive rayon fiber REC-Bmade by UNITICA CO., LTD. is used as a pile fabric, is wound spirally asthe brush 247 b around the core metal 247 a with a diameter of 6millimeters to form the brush roller 220B having an outer diameter of 14millimeters and a length of 250 millimeters along the axial direction.Note that the core metal 247 a also acts as an electrode. The brush hasa density of 300 deniers/50 filaments and 155 threads per one squaremillimeter. The brush 202B is inserted into a pipe having a diameter of12 millimeters by rotating in one direction and fitted in such a waythat the brush and the pipe are concentric. Hair of the brush can bebent on one side by leaving the brush in a high temperature and highhumidity atmosphere. The resistance value of the brush roller 220B is1×10⁵ ohms for an applied voltage of 100 volts.

[0224] This resistance value is calculated from the current that passeswhen the brush roller 220B is brought into contact with the metal drumhaving a diameter of 30 millimeters with a nip width of 3 millimetersand a voltage of 100 volts is applied to the core metal 247 a. Theresistance value of the brush roller has to be 10⁴ ohms or more so thateven if a defective part of the low withstand voltage such as a pinholeis produced on the image carrier drum as a charged body, there is nopoor charging of the charging nip due to an excessive leakage current inthis part and defective image forming is prohibited. The resistancevalue of the brush roller has to be 10⁷ ohms or less to injectsufficient charge on the surface of the image carrier drum.

[0225] The material for the brush includes REC-C, REC-M1, REC-M10 inaddition to REC-B made by UNITICA CO., LTD, SA-7 made by TORAY CO., LTD,Thunderon made by NIHON SANMO CO., LTD, Belltron made by KANEBO CO.,LTD, Clacarbo made by KURARAY CO., LTD, a material obtained bydispersing carbon into rayon, and Lobal made by MITSUBISHI RAYON CO.,LTD. It is preferable that a line of brush is in a range of 3 deniers to10 deniers, and the brush is in a range of 10 filaments to 100 filamentsper bunch, and has 80 threads to 600 threads per millimeter. Thepreferable length of brush hair is in a range of 1 millimeter to 10millimeters.

[0226] The brush roller 220B in the example is driven to rotate at aprescribed circumferential velocity (speed of the surface) in a reversedirection (counter direction) to the rotating direction of the imagecarrier drum 202. The brush roller 220B is in contact with the surfaceof the image carrier drum 202 with a different speed as that of thedrum. A power supply 250 applies a prescribed charging voltage to thebrush roller 220B, and the rotating image carrier drum is chargeduniformly to a prescribed polarity and electric potential by the brushroller in contact with the drum. In the example, the brush roller 220Bcarries out the contact charging to the image carrier drum dominantly bydirect injection charging, and the surface of the image carrier drum ischarged to almost the same electric potential as the applied chargingvoltage to the brush roller. The damper is fitted inside the imagecarrier drum 202 in FIG. 19 as well. Due to the effect of the damper,the generation of noise in the image carrier drum 202 is reduced even ifthe charging voltage in which ac voltage is superimposed on dc voltageis applied to the brush roller 220B.

[0227] In an example in FIG. 20, a charging unit that uses a magneticbrush is provided adjacent to the image carrier drum 202. A magneticbrush MB is arranged such that it is in contact with the peripheralsurface of the image carrier drum 202 with a prescribed nip.

[0228] A magnetic brush unit 220C in the example includes a non-magneticsleeve 257 a that supports the magnetic brush MB and a magnetic roller(not shown) incorporated in the non-magnetic sleeve 257 a. Various typesof ferrite particles like Zn—Cu ferrite can be used as particles for themagnetic brush. More specifically, the magnetic brush is formed asfollows. The Zn—Cu ferrite particles of an average particle size: 25 μmare mixed with Zn—Cu ferrite particles of an average particle size: 10μm in the ratio of weights 1:0.05 respectively. The ferrite particles ofan average particle size 25 μm which have peaks in respective positionsof the average particle size, are coated with a resin layer of mediumresistance to give magnetic particles. The sleeve 257 a is coated withthe coated magnetic particles by a thickness of 1 millimeter to form themagnetic brush.

[0229] The magnetic particles are carried on the sleeve 257 a bymagnetic force of the magnetic roller that is incorporated in the sleeve257 a. Such a magnetic brush MB forms a charging nip having a width ofabout 5 millimeters (width of the direction of rotation) between themagnetic brush MB and the image carrier drum 202, and enables to adjustthe gap between the sleeve 257 a that holds the magnetic particles andthe image carrier drum 202 to about 500 μm.

[0230] Moreover, it is preferable that the non-magnetic sleeve 257 a isrotated so that the surface of the sleeve 257 a moves in the directionopposite to the direction of moving of the surface of the image carrierdrum at a speed double with respect to the peripheral velocity of theimage carrier drum. It is also preferable that the magnetic brush ismade to scrape the surface of the image carrier drum, and that the imagecarrier drum and the magnetic brush are in uniform contact with eachother. A prescribed charging voltage is applied to the sleeve 257 a bythe power source 250 and the image carrier drum is charged uniformly toa prescribed polarity and electric potential through the magnetic brushMB. The damper is fitted inside the image carrier drum 202 in FIG. 20 aswell. Due to the effect of the damper, the generation of noise in theimage carrier drum 202 is reduced even if the charging voltage in whichac voltage is superimposed on dc voltage is applied to the drum 202 byusing a contact type charging unit like the magnetic brush unit 220C inthe example.

[0231] The present invention can be applied to a color image formingapparatus in which plurality of image carrier drums, i.e. photoreceptordrums are lined up. Moreover, the present invention is also applicableto any types of image forming apparatuses like a printer, a facsimile, acopying machine, and a multifunction machine of these apparatuses.

[0232] Thus, the example of the image carrier drum that is formed with aphotoreceptor drum and is provided with the damper inside the imagecarrier drum is explained here. However, even in a case of the imagecarrier drum formed with an intermediate transfer drum to which thetoner image is transferred from the photoreceptor, the generation ofnoise from the intermediate transfer drum can be reduced effectively byproviding the damper inside the intermediate transfer drum. Moreover,the generation of noise can be reduced by providing the damper insidethe roller that supports the photoreceptor in the form of an endlessbelt and the intermediate transfer belt.

[0233] Thus, according to the second embodiment, the generation of noisecan be effectively reduced even if the toner having a low melting pointis used.

[0234] A third embodiment of this invention will be explained below.

[0235]FIG. 21 is a cross section of an image forming unit of an imageforming apparatus provided with an image carrier drum according to thethird embodiment. An image carrier drum 202 in the figure is aphotoreceptor drum which includes a photosensitive layer provided on anouter peripheral surface of a circular cylindrical tube made of aconductive metal like aluminum. The image carrier drum 202 is supportedby a shaft 301 that extends through inside the image carrier drum 202 asexplained later. Both ends of the shaft 301 along its length aresupported by a case 219 of an image forming module 218. The imagecarrier drum 202 supported by the shaft 301 is rotated by a drive motor(not shown) in a clockwise direction as shown in FIG. 21. Duringrotation of the image carrier drum 202, a charging unit formed with acharging roller 220 rotatably supported by the case 219 rotates whilebeing in contact with the outer peripheral surface of the image carrierdrum 202. The surface of the image carrier drum 202 is charged to aprescribed polarity by applying a charging voltage to the chargingroller 220.

[0236] A modulated laser beam L emitted from an exposing unit (notshown) is irradiated on the surface of the image carrier drum 202 afterbeing charged to form an electrostatic latent image on the image carrierdrum. The exposing unit is provided separately apart from the imageforming module 218. This electrostatic latent image is visualized as atoner image by a developing unit 222. The toner image is carried on atransfer belt 208 and is transferred to a transfer paper P that travelsin a direction of an arrow A by an action of a transfer brush 209. Thetoner image having been transferred to the transfer paper P is fixed onthe transfer paper by a fixing unit (not shown). A residual toner on theimage carrier drum after the transferring of the toner image iseliminated by combined action of a charging brush 229 and a cleaningblade 230 of a cleaning unit 227.

[0237] The developing unit 222 includes a developing case 223 that isformed with a part of the case 219 of the image forming module 218 and adeveloping roller 224 that is rotatably supported by the developing case223. The developing case 223 contains developer D. The developer D iscarried on the rotating developing roller 224 and transferred, and theelectrostatic latent image is visualized by the transferred developer.In this case, a two-component developer, which includes toner andcarrier, is used as the developer. When a decrease in toner density ofthe developer is detected, the toner is replenished from a tonercontainer 233. The cleaning unit 227 includes a cleaning case 228 thatis also formed with a part of the case 219 of the image forming module218. The cleaning brush 229 and the cleaning blade 230 are supported bythe cleaning case 228. The toner recovered from the image carrier drum202 is returned to the toner container 233 through a toner carrier tube231 connected to the case 219.

[0238] Thus, in the image forming apparatus shown in FIG. 21, the imagecarrier drum 202 and the image forming units provided around the drum202 such as the charging roller 220, the developing roller 224, thecleaning brush 229, the cleaning blade 230 are integrally assembled tothe case 219 and the image forming module 218 is formed thereby. Theimage forming module 218 is detachable from a casing (not shown) of theimage forming apparatus and can be replaced by a new image formingmodule when the module reaches end of its life.

[0239]FIG. 22 is a longitudinal cross section of the image carrier drum202. Ordinary flanges 303 and 303A are fitted to ends of the imagecarrier drum 202 in its axial direction of this figure. The shaft 301passes through the flanges 303 and 303A and extends through inside theimage carrier drum 202. The image carrier drum 202 is supported by theshaft 301 through the flanges 303 and 303A. The shaft 301 is disposedconcentrically with the image carrier drum 202 and extends through thecenter of the image carrier drum 202.

[0240] A gear 305 is integrated on the outer periphery of the flange303. A counter gear (not shown) engages with the gear 305. A drive motor(not shown) rotates the flange 303 by transmitting the rotations throughthe gear 305 and the counter gear. The rotations of the flange 303 aretransmitted to the image carrier drum 202, and the image carrier drum202 rotates around the axis of its center. As shown in FIG. 23, a notch306 is formed at an edge of the image carrier drum 202. A protrusion 307provided on the flange 303 is engaged in the notch 306 therebytransmitting the rotation of the flange 303 to the image carrier drum202. The flanges 303 and 303A may be press fitted into the ends of theimage carrier drum 202, or may be fixed to the image carrier drum 202with an adhesive. The flanges 303 and 303A may also be engaged with theimage carrier drum 202 by clearance fit. When the flanges 303 and 303Aare engaged by the clearance fit, it is necessary to hold the flanges byusing thrust stoppers (not shown), which are provided to stop theflanges 303 and 303A from moving in the axial direction of the imagecarrier drum 202 and coming off. A sidewall of the case 219 shown inFIG. 21 can be used as the thrust stopper.

[0241] The shaft 301 passing through the flanges 303 and 303A may befixed to the flanges by press fit. The shaft 301 may also be engagedwith the flanges 303 and 303A such that the flanges can rotate freelyaround the shaft 301. In the former case, the shaft 301 rotates togetherwith the flange 303, flange 303A, and the image carrier drum 202 whereasin the latter case the shaft 301 does not rotate. In either of thecases, the shaft 301 is supported by the case 219 as shown in FIG. 21.

[0242] The charging roller 220 and the cleaning blade 230 are in contactwith the outer peripheral surface of the image carrier drum 202 as shownin FIG. 21. When a charging voltage having ac voltage superimposed on dcvoltage is applied to the charging roller 220, the charging roller 220vibrates due to the application of the ac voltage. Further, the cleaningblade 230 vibrates due to stick-slip during rotation of the imagecarrier drum 202. These vibrations are transmitted to the drum 202, andthe drum 202 vibrates. If these vibrations become strong, then noise isproduced.

[0243] Therefore, a damper 204 (204G) is disposed inside the imagecarrier drum 202 of this embodiment as shown in FIG. 21 and FIG. 22. Thedamper 204G shown in the figures is in the form of a cup having almostU-shaped longitudinal cross sectional form. The shaft 301 passes througha hole 310 that is made in the bottom wall of the damper 204G. Thedamper 204G can be made of an appropriate material like an elasticmaterial, a rigid material such as rubber, resin, and metal, or acombination of these materials. The damper 204 having an outer diameterslightly smaller than an inner diameter of the image carrier drum 202 isused, and such a damper 204 may be fixed to the inner wall surface ofthe image carrier drum 202 with an adhesive. Alternatively, the damper204 having an outer diameter before being inserted into the drum 202that is slightly bigger than an inner diameter of the drum 202 is used.When such a damper 204 is inserted inside the drum 202, the damper 204may be elastically deformed in the direction in which the diameter iscontracted. Thus, the damper 204 may be pressed against the inner wallsurface of the drum 202 and fixed to the drum 202.

[0244] Thus, a cylinder unit 312 is integrally formed with the cylinder(the image carrier drum 202 in the example), a shaft that supports thecylinder, and a damper that is disposed inside the cylinder. The shaft301 passes through the cylinder and further extends. In the exampleshown in FIG. 22, the pair of flanges 303 and 303A is also included inthe cylinder unit 312. The damper 204 is provided inside the imagecarrier drum 202, which makes it possible to reduce the vibrations inthe image carrier drum 202 and effectively suppress the generation ofnoise.

[0245] The image carrier drum 202 goes on deteriorating with time andwhen it reaches end of its life, the image forming module 218 shown inFIG. 21 is removed from the body of the apparatus and replaced by a newimage forming module. The image forming module 218 removed from the bodyof the apparatus is recycled. That is, the cylinder unit 212 is removedfrom the case 219 of the image forming module 218 and disassembled intocomponents. The components that can be reused in the existing conditionare reused as they are, and the other components are subjected toprescribed recycling processing and are provided for reuse.

[0246] To facilitate the recycling of the cylinder unit 212, i.e. to beable to remove the damper 204 from the image carrier drum 202, thecylinder unit 212 is structured as follows. As shown in FIG. 22, aprotrusion 313 having a diameter bigger than that of the shaft 301 isintegrated with the shaft 301. A portion 311 of the damper 204 facingthe protrusion 313, is positioned such that the portion 311 is incontact with the protrusion 313. The flange 303A on the other side ispulled out from the shaft 301 and removed. In the case where the flange303A is fixed to the image carrier drum 303 with an adhesive, the flange303A is applied with force to break the adhesive and is separated fromthe shaft 301 and the image carrier drum 202.

[0247] Then, the shaft 301 is moved in the direction shown by an arrow Bin FIG. 22, i.e. in the axial direction of the image carrier drum 202.When the shaft 301 is moved, the protrusion 313 that is fixed to theshaft 301 comes in contact with a portion 311 of the damper 204(hereinafter “contacting portion”) and pushes the area in the directionof the arrow B. Due to this, the damper 204 moves in the axial directionof the image carrier drum, i.e. the direction of the arrow B togetherwith the shaft 301. In the case where the damper 204 is fixed to theinner wall surface of the image carrier drum 202 with an adhesive, thedamper 204 is pushed in the direction of the arrow B to break theadhesive, and is moved in the direction of the arrow B.

[0248] While moving the damper 204, the shaft 301 slides with respect tothe flange 303. As shown in FIG. 24, when the shaft 301 is moved furtherin the direction of the arrow B, the damper 204 moving together with theshaft 301 pushes the flange 303, and therefore the flange 303 is removedfrom the image carrier drum 202. In this case also, when the flange 303is fixed to the image carrier drum 202 with an adhesive, by applying anexternal force to the flange, the adhesive is broken. Moreover, when theshaft 301 is moved further in the direction of the arrow B, the damper204 is eventually removed from the image carrier drum 202. In the casewhere the flange 303 is fixed to the image carrier drum 202 by clearancefit, the flange 303 can be removed from the image carrier drum 202before the damper 204 comes in contact with the flange 303. Thus, justby pulling out the shaft 301, the damper 204 and the flange 303 can beremoved from the image carrier drum 202 thereby enabling disassemble ofthe cylinder unit with ease and at a low cost without using any specialtools.

[0249] As explained above, the cylinder, the shaft 301, and the damper204 are assembled such that when the shaft 301 is pulled out from thecylinder as the image carrier drum 202, the damper 204 moves in theaxial direction of the cylinder together with the shaft 301 and isremoved from the cylinder. Moreover, in the cylinder unit 312, theprotrusion 313 protruding in the radial direction of the shaft 301 isprovided on the shaft 301. The damper 204 has the contacting portion 311that comes in contact with the protrusion 313 when the shaft 301 ispulled out from the cylinder. The protrusion 313 is brought into contactwith the contacting portion 311 and the damper 204 is moved togetherwith the shaft 301 thereby simplifying the structure of the cylinderunit 312.

[0250] Furthermore, the contacting portion 311 of the damper 204 ispositioned at the front end in the movement direction of the damper 204.Therefore, if the damper 204 is made of an elastic material, the damper204 is deformed by reducing its diameter when the shaft 301 and thedamper 204 move in the direction of the arrow B, which allows the damper204 to be easily moved inside the image carrier drum. Assume that theprotrusion 313 fixed to the shaft 301 is structured such that theprotrusion 313 pushes the rear end of the damper 204 made of an elasticmaterial in the movement direction of the damper 204. The frictionalforce that acts between the damper 204 and the inner wall surface of theimage carrier drum is exerted on the damper 204. Due to this frictionalforce, the damper 204 expands in the radial direction and cannot bemoved smoothly. However, since the contacting portion 311 is at thefront end of the damper 204 in the direction of its movement, there isno hindrance to the movement of the damper.

[0251] The shaft 301, the damper 204, the flange 303, and the flange303A which are disassembled in the above manner, can be reused as theyare only by cleaning these components. Moreover, since the damper 204 inthe cylinder unit 312 is disposed in the space surrounded by the imagecarrier drum 202, the flange 303, and the flange 303A, the damper 204 isnot contaminated by either of dust and toner during the use of thecylinder unit 312. Therefore, the damper 204 can also be reused withoutcleaning after it is separated from the image carrier drum.

[0252] The assembling of the cylinder unit 312 is also facilitated. Forexample, the damper 204 is disposed on the left side of the imagecarrier drum 202 in FIG. 22 and the shaft 301 on which the flanges 303and 303A are not fixed is inserted inside the image carrier drum 202from the left end of the drum 202. While inserting the shaft 301, theshaft 301 is passed through the hole 310 of the damper 204, and thecontacting portion 311 of the damper 204 is pushed by the protrusion 313provided on the shaft 301. While pressurizing the damper 204 in thedirection of the arrow B in FIG. 22, the shaft 301 together with thedamper 204 is inserted into the image carrier drum 202. Then, theflanges 303 and 303A are fitted to the ends of the shaft 301 and alsofitted on the ends of the image carrier drum 202 thereby fitting thedamper 204 inside the image carrier drum 202.

[0253] Further, as shown in FIG. 25 and FIG. 27, the damper 204 can alsobe integrally coupled to the shaft 301. FIG. 25 illustrates an exampleof fixing a hollow circular cylindrical shaped damper 204 to the shaft301, and FIG. 26 illustrates an example of using a damper 204 in which aplurality of circular discs 204A are integrated with a base 204B andfixing the base 204B to the shaft 301. FIG. 27 illustrates an example offixing a plurality of circular shaped discs 204C to the shaft 301 toform a damper 204.

[0254] For disassembling the components of cylinder units 312 shown inFIG. 25 to FIG. 27, when the shaft 301 is moved in the direction of thearrow B after the flange 303A is separated from the shaft 301 in thesame manner as explained above, the damper 204 that is integrallycoupled to the shaft 301 also moves with the shaft 301, which allows theflange 303 and the damper 204 to be separated from the image carrierdrum 202. The rest of the structures shown in FIG. 25 to FIG. 27 arepractically similar to those shown in FIG. 21 to FIG. 24.

[0255] The effect similar to that of the cylinder units 312 shown inFIG. 25 to FIG. 27 can be achieved also by fixing a solid cylindricaldamper to the shaft 301. However, when the solid damper is moved insidethe image carrier drum 202, the solid damper undergoes a considerableamount of frictional force from the inner wall surface of the imagecarrier drum 202, and therefore smooth movement of the damper becomesdifficult. When the dampers 204, shown in FIG. 25 to FIG. 27, are madeof an elastic material in particular, the dampers 204 undergo elasticdeformation easily when they are moved inside the image carrier drum202. Therefore, the frictional force exerted by the inner wall surfaceof the image carrier drum 202 decreases and the dampers 204 can be movedeasily.

[0256] Moreover, in the example shown in FIG. 22, when the diameter ofthe image carrier drum 202 is small, the diameters of the damper 204 andthe protrusion 313 also become smaller, and a contact area between theprotrusion 313 and contacting portion 311 of the damper 204 becomessmaller. Therefore, when the shaft 301 is moved in the direction of thearrow B, the pressure per unit area of the contact surface between theprotrusion 313 and the contacting portion 311 increases. Therefore,especially in the case of the damper 204 made of an elastic material,the portion of the damper 204 pushed by the protrusion 313 undergoesconsiderable elastic deformation. Due to the elastic deformation, theforce is not conveyed properly from the protrusion 313 to the damper204, and therefore the damper 204 may not be moved smoothly. To avoidthis, the damper 204 is integrally coupled to the shaft 301 to make itmove easily together with the shaft 301 when the shaft 301 is pulled outfrom the cylinder as shown in the examples in FIG. 25 to FIG. 27. Thus,the damper 204 can reliably be moved and can be removed from the imagecarrier drum 202 easily.

[0257] The cylinder unit 312 has a pair of flanges 303 and 303A fittedto the ends of the cylinder formed with the image carrier drum 202 inthe axial direction. The cylinder is supported by the shaft 301 throughthese flanges 303 and 303A. The shape of the damper is set so that thedamper 204 moves in the axial direction of the cylinder to come incontact with the flange 303 and pushes the flange 303, and then theflange 303 is removed from the cylinder. Therefore, as explained above,the flange 303 can be separated from the cylinder just by pulling outthe shaft 301. Thus, the workability can be enhanced.

[0258] The damper 204 can be formed by an appropriate material asexplained above. As shown in FIG. 28, in a case of pulling out the shaft301 from the image carrier drum 202, if a portion 314 of the dampercoming in contact with the flange 303 is made of a rigid material, bybringing the portion 314 of the damper into contact with the flange 303and pressurizing the flange 303, the force can be appropriately conveyedto the flange 303. Thus, the flange can be separated easily from theimage carrier drum 202. The portion 314 of the damper can be made of ABSresin or metal having a Young's modulus of about 2 to 3 GPa.

[0259] When the portion 314 of the damper is made of the rigid material,if the speed at which the shaft 301 is pulled out is high, the portion314 of the damper impacts against the flange 303 and may damage theflange 303. In a case of such concern, the portion 314 of the dampercoming in contact with the flanges 303 may be made of an elasticmaterial. For example, the portion 314 of the damper is made of rubberhaving a Young's modulus of about 0.5 to 1.5 MPa. Thus, even when theportion 314 impacts against the flange 303, the damage of the flange 303can be prevented and reused without any trouble.

[0260] As shown in FIG. 29, the flange 303 can be structured to have afirst cylinder member 315 that fits to the ends of the cylinder formedwith the image carrier drum 202 in the axial direction and a secondcylinder member 316 that fits into the first cylinder member 315. Inthis example, a gear 305 is formed on the first cylinder member 315.FIG. 30 is an exploded perspective view of the first cylinder member 315and the second cylinder member 316. To fit the flange 303 to the imagecarrier drum 202, as shown in FIG. 31, the first cylinder member 315 isfitted into the end of the image carrier drum 202 and then the secondcylinder member 316 is fitted into the first cylinder member 315. Inthis case, assume that an outer diameter of the second cylinder member316 before it is fitted into the first cylinder member 315 is D1, athickness of a part of the first cylinder member 315 that is inserted inthe image carrier drum 202 is T, and an inner diameter of the imagecarrier drum 202 is D2. Each diameter and thickness are set so as to beD1+2T>D2. Thus, when the second cylinder member 316 is fitted in thefirst cylinder member 315 as shown in FIG. 29, the part of the firstcylinder member 315 that is inserted into the image carrier drum 202 isin press contact with the inner wall surface of the image carrier drum202 and the whole of the flange 303 is fixed to the image carrier drum202.

[0261] Thus, the second cylinder member 316 is fitted in the firstcylinder member 315, the first cylinder member 315 is made to be inpressed contact with the inner wall surface of the cylinder of the drum202 and the flange is fixed on the cylinder. A plurality of slits 340 isformed in the first cylinder member 315 as shown in FIG. 30, andtherefore the first cylinder member 315 can be pressed easily againstthe inner wall surface of the image carrier drum 202 by the secondcylinder member 316. The shaft 301 is passed through a hole 342 in thesecond cylinder member 316 as shown in FIG. 29. The shaft 301 can beassembled with the image carrier drum 202 after fixing the flange 303 tothe image carrier drum 202. The shaft 301 can also be inserted into theimage carrier drum 202 before fixing the flange 303 to the image carrierdrum 202. For the flange 303A (FIG. 22, FIG. 25), any of the flangesshown in FIG. 29 to FIG. 31 can be used.

[0262] When the flange 303 is structured in this manner, if the diameterof the front end of the damper 204 that faces the flange 303 is madesmaller as shown in FIG. 29 and the damper 204 is moved together withthe flange 303 in the direction of the arrow B, then it is preferable tostructure such that a front end surface 341 of the front end comes incontact only with the second cylinder member 316. That is, thearrangement is made such that the damper 204 moves in an axial directionof the cylinder, the front end surface 341 of the damper 204 comes incontact only with the second cylinder member 316, and pushes the secondcylinder member 316. With this arrangement, the second cylinder member316 and the first cylinder member 315 are separated apart from eachother due to the second cylinder member 316 pushed by the damper 204.Thus, the first cylinder member 315 and the second cylinder member 316can be removed from the image carrier drum 202 without applying heavyload on them. This prevents causing of any damage to the first cylindermember 315 and the second cylinder member 316 thereby enabling theirreuse without any processing after disassembling.

[0263] According to the embodiment, the damper 204 can be integratedwith the cylinder including the image carrier drum 202 as an integralassembly by press fitting the damper on the inner wall surface of thecylinder due to elastic property of the damper 204. When the damper 204is fixed to the image carrier drum 202 without using any adhesivematerial, the shaft 301 can be pulled out from the image carrier drum202 easily thereby facilitating disassembling of the image carrier drum202.

[0264] As explained above, the cylinder of the image carrier drum 202,the pair of the flanges 303 and 303A, and the shaft 301 are assembledtogether to rotate as an integrated assembly by press fitting theflanges 303 and 303A to the shaft 301 so as to be fixed to each other.Therefore, the flanges 303 and 303A cannot rotate around the shaft 301since they are fixed. This prevents the sliding contact between theshaft 301 and the flanges 303 and 303A thereby preventing wearing awayof the three. Thus, the shaft 301 and the flanges 303 and 303A can bereused after disassembling without carrying out any special machiningprocess on them.

[0265] In the embodiment, the cylinder is the image carrier drum 202 onwhich a toner image is formed. In other words, although the cylinder inthis example is a photoreceptor drum, when the cylinder is any deviceother than the image carrier drum, these structures can be employed.Concretely, the cylinder includes an image carrier drum that includesintermediate transfer body on which a toner image formed on thephotoreceptor drum is transferred, a charging roller, a developingroller, transfer paper carrier roller, and any other cylinder formed asa support for a structure.

[0266] Moreover, the image forming apparatus in FIG. 21 includes theimage carrier drum 202, and the image forming module that is assembledby integrating the image forming elements like the charging roller 220,the developing roller 224, the cleaning brush 229, and the cleaningblade 230 to form the image on the image carrier drum 202. It is anormal practice to reduce the size and weight of this image formingmodule to make it easy to handle.

[0267] Therefore, since small sized elements are used in the imageforming module, the life of the image forming module is short. In theimage forming apparatus in FIG. 21, an arrangement is made to replenishthe toner container 233 with toner. However, when there is noarrangement for replenishment of the toner and when the structure ismade such that the image forming module is to be replaced after thetoner in the developing unit gets exhausted, the life of the imageforming module becomes further short. The short life of the imageforming module implies increased number of the image forming modulesthat are manufactured and are in the market. Therefore, it is importantto facilitate the disassembling of the cylinder unit 312 and improverecycling. By structuring the cylinder unit 312 as mentioned in theembodiment, the cylinder unit 312 can be easily recycled, and the demandcan be surely satisfied.

[0268] The cylinder unit can also be made discretely detachable from themain body of the image forming apparatus. In this case, it is a normalpractice to set the life of the image carrier drum longer than that ofthe image forming unit that forms an image on the image carrier drum andto go on replacing the image carrier drum while the image formingapparatus is being used. In such a case also, by structuring thecylinder unit 312 as mentioned in this embodiment to improve recycling,it is possible to reuse the components of the cylinder unit 312 easily.

[0269] Thus, according to the third embodiment, the recycling isfacilitated by structuring the cylinder unit such that it can be easilydisassembled.

[0270] A fourth embodiment of this invention will be explained below.

[0271]FIG. 32 is a schematic diagram of an image forming section of theimage forming apparatus that uses an image carrier drum according to thefourth embodiment. An image carrier drum 202 in the figure is aphotoreceptor drum which includes a circular tube made of a conductivemetal like aluminum with a photosensitive layer provided on an outerperipheral surface. The image carrier drum 202 is rotatably supported bya case 219 of a process cartridge 218 and is rotated by a drive motor(not shown) in the clockwise direction in FIG. 32. A charging unitincluding a charging roller 220 rotatably supported by the case 219 isin contact with the image carrier drum 202 and rotates. By applying acharging voltage to the charging roller 220, a surface of the imagecarrier drum 202 is charged to a prescribed polarity.

[0272] A modulated laser beam L is irradiated on the surface of theimage carrier drum 202 after being charged, the beam being emitted froman exposing unit (not shown) provided separately apart from the processcartridge. Thereby an electrostatic latent image is formed on the imagecarrier drum 202. This electrostatic latent image is visualized as atoner image by a developing unit 222. The toner image is carried on atransfer belt 208 and is transferred to a recording medium P such as atransfer paper that travels in a direction of an arrow A, by an actionof a transfer brush 209 as an example of the transfer unit. The tonerimage having been transferred to the recording medium P is fixed on therecording medium by the fixing unit (not shown). A residual toner on theimage carrier drum that remains after the transferring of the tonerimage is eliminated by combined action of a cleaning brush 229 and acleaning blade 230 of a cleaning unit 227.

[0273] The developing unit 222 includes a developing case 223 formedwith a part of the case 219 of the process cartridge 218 and adeveloping roller 224 rotatably supported by the developing case 223.The developing case 223 contains developer D. The rotating developingroller 224 carries and conveys the developer D. The conveyed developervisualizes the electrostatic latent image. In this case, a drytwo-component developer including toner and carrier, is used asdeveloper, and when a decrease in toner density of the developer isdetected, the toner is replenished from a toner container.

[0274] The cleaning unit 227 includes the cleaning case 228 also formedwith a part of the case 219 of the process cartridge 218. The cleaningbrush 229 and the cleaning blade 230 are supported by the cleaning case228. The toner recovered from the image carrier drum 202 is returned tothe toner container 233 through a toner carrier tube 231 connected tothe case 219.

[0275]FIG. 33 is a longitudinal cross section of the image carrier drum202. Flanges 303 and 303A are fitted at each end of the image carrierdrum 202 in the axial direction. The flanges 303 and 303A are rotatablysupported by the case 219 (FIG. 32), and the image carrier drum 202 isthereby rotatably supported by the case 219. It is possible to omit oneof the flanges 303 and 303A. It is also possible to omit both theflanges, and both ends of the image carrier drum 202 can be rotatablysupported directly by the case 219. When it is necessary to distinguishthese flanges 303 and 303A from each other, the flange 303 is referredto as a first flange and the flange 303A is referred to as a secondflange.

[0276] A gear 305 is integrated on the outer peripheral surface of thesecond flange 303A. A counter gear, which is not shown in the figure, isengaged with the gear 305. A drive motor, which is also not shown in thefigure, rotates the second flange 303A by transmitting the rotationsthrough these gears. The rotations of the flange 303A are transmitted tothe image carrier drum 202, and the drum 202 rotates around the centralaxis of the flange 303A. A notch 306 is made at an end of the imagecarrier drum 202 as shown in FIG. 23. A protrusion 307 provided on thesecond flange 303A is engaged in the notch 306 thereby preventingrelative rotation of the second flange 303A and the image carrier drum202 and transmitting the rotation of the flange 303A to the imagecarrier drum 202.

[0277] The flanges 303 and 303A may be press fitted into openings at theends of the image carrier drum 202 or may be fixed to the image carrierdrum 202 with an adhesive. The flanges 303 and 303A can also be engagedwith the image carrier drum by clearance fit. When the flanges 303 and303A are engaged by clearance fit, it is necessary to hold the flangesby using thrust stoppers not shown in the figure, which are provided tostop the flanges 303 and 303A from moving in the axial direction of theimage carrier drum 202 and from being removed from the drum 202. Asidewall of the case 219 shown in FIG. 32 can be used as a thruststopper.

[0278] The charging roller 202 and the cleaning blade 230 are in contactwith the outer peripheral surface of the image carrier drum 202 as shownin FIG. 32. When a charging voltage having ac voltage superimposed on dcvoltage, is applied to the charging roller 220, the charging roller 220vibrates due to the application of the ac voltage. Further, the cleaningblade 230 vibrates due to stick-slip during rotation of the imagecarrier drum 202. These vibrations are transmitted to the image carrierdrum 202, due to which the drum 202 vibrates. When these vibrationsbecome strong, noise is produced.

[0279] Therefore, a damper 404 is disposed inside the image carrier drum202 of this example as shown in FIG. 32 and FIG. 33. The damper 404includes a cylinder 417 having an outer peripheral surface 414 that isfixed to the inner peripheral surface of the image carrier drum 202, anda sidewall 410. The damper 404 is in the form of a cup having almostU-shaped longitudinal cross sectional form. An end of the damper 404opposite to the sidewall 410 is kept open as an open end.

[0280] The damper 404 can be made of an appropriate material such as anelastic material, a rigid material such as rubber, resin, and metal, ora combination of these materials.

[0281] The damper 404 having an outer diameter slightly smaller than aninner diameter of the image carrier drum 202 may be used and fixed tothe inner surface of the image carrier drum 202 with an adhesive. Thedamper 404 having an outer diameter before being inserted into the drum202 that is slightly bigger than an inner diameter of the drum 202 maybe used and inserted into the image carrier drum 202. When the damper404 is inserted into the drum 202, the damper 404 undergoes elasticdeformation in the direction of contraction of the diameter. Thus, thedamper 404 can be fixed inside the image carrier drum 202 by making apressed contact with an inner surface of the drum 202.

[0282] Thus, the damper 404 mounted inside the image carrier drum 202 isheld inside the image carrier drum 202 due to the pressed contact withthe inner surface of the image carrier drum 202. The pressed contact isattributed to the elasticity of the material of the damper.Alternatively, the damper 404 is fixed on the inner wall surface of theimage carrier drum 202 with an adhesive. The damper 404 may also befixed on the inner wall surface of the image carrier drum 202 using bothelasticity and the adhesive.

[0283] The damper 404, which is provided inside the image carrier drum202, reduces vibrations of the image carrier drum 202 and effectivelysuppresses the generation of noise.

[0284] Moreover, in the image forming apparatus of this example, anintegrated drum unit 434 is structured by assembling the image carrierdrum 202 with the damper 404 that is mounted inside the drum and thepair of flanges 303 and 303A. It is also possible to structure theintegrated drum unit 434 without the flanges 303 and 303A. The drum unit434 includes at least the image carrier drum 202 and the damper 404.

[0285] Further, in the image forming apparatus of this example, theprocess cartridge 218 is structured by assembling the drum unit 434integrated with the image forming units such as the charging roller 220,the developing unit 222, the cleaning unit 227, which are disposedaround the drum unit 434. Suitable image forming units can be selectedfor forming the process cartridge 218. In short, the process cartridgeincludes a drum unit and at least an image forming unit that forms atoner image on an image carrier drum of the drum unit. The processcartridge is detachable from the main body of the image formingapparatus. The image forming apparatus of this example includes eitherof the process cartridge 218 and the drum unit 434.

[0286] The image carrier drum 202 goes on deteriorating with time andwhen it reaches end of its life, the process cartridge 218 shown in FIG.32 is removed from the main body of the image forming apparatus andreplaced by a new process cartridge. The process cartridge 218 removedfrom the main body of the image forming apparatus is recycled. Inrecycling process, the image carrier drum 202 is removed from the case219 of the process cartridge 219. The image carrier drum 202 and thecomponents that are assembled together with the drum are disassembled.The components that can be reused in the existing condition are reusedas they are, and the rest of the components are subjected topredetermined machining or treatment process, and are provided forreuse.

[0287] To facilitate the recycling of the image carrier drum 202, thedamper 404, and the flanges 303 and 303A that are assembled with thedrum, the following method is employed to easily assemble anddisassemble these components.

[0288]FIG. 34 and FIG. 35 are cross sections of how a damper 404 isfixed to an image carrier drum 202. In the example shown here, an imagecarrier drum 202 without flanges 303 and 303A fixed on it is prepared. Asidewall 410 of the damper 404 is made to face an opening 411 on one endin the axial direction of the image carrier drum 202 as shown in FIG.34. In the examples shown in FIG. 34 and FIG. 35, the damper 404 is madeof an elastic material like rubber. An outer diameter of the damper 404before being inserted into the image carrier drum 202 is set to beslightly bigger than an inner diameter of the image carrier drum 202.

[0289] In the state as shown in FIG. 34, a force imparting member 413 inthe form of a rod is inserted into a cylinder 417 of the damper 404 inthe direction of an arrow B from the opening end of the damper 404. Afront-end 413A of the force imparting member 413 is brought into contactwith the sidewall 410 of the damper 404 and the force imparting member413 is pushed further in the direction of the arrow B along the axialdirection of the image carrier drum 202. Thus, the damper 404 is thrustinside the image carrier drum 202 as shown in FIG. 35 and moved up tothe position shown in FIG. 33. Then, the force imparting member 413 ispulled in a direction opposite to that of the arrow B and pulled outfrom the image carrier drum. Thus, the damper 404 having the outerdiameter before being inserted into the drum 202 that is slightly biggerthan an inner diameter of the image carrier drum 202, can be insertedand mounted inside the image carrier drum 202 with ease.

[0290] The damper 404 mounted inside the image carrier drum 202 is fixedto the image carrier drum 202 by pressing an outer peripheral surface414 of the cylinder 417 against the inner peripheral surface of the drum202 by the elasticity. The first flange 303 and the second flange 303Aare fixed on the opening 411 and an opening 412 on both ends in theaxial direction of the drum 202 respectively as shown in FIG. 33. Theimage carrier drum 202 thus formed is assembled with the case 219 shownin FIG. 32 and used.

[0291] The outer peripheral surface 414 of the damper 404 can also befixed to the inner peripheral surface of the image carrier drum 202 withan adhesive. When the damper 404 is made of a rigid material, the damper404 can be inserted into the image carrier drum 202 and fixed to theinner peripheral surface of the image carrier drum 202 in the samemanner as explained above.

[0292] When the image carrier drum 202 and the damper 404 are to bedisassembled, first of all the first flange 303 is removed from theimage carrier drum 202 as shown in FIG. 33. When the flange 303 is fixedto the image carrier drum 202 with an adhesive, a force is applied tothe flange 303 to break the adhesive, and the flange 303 is separatedapart from the image carrier drum 202. Then, as shown in FIG. 36, theforce imparting member 413 is inserted into the image carrier drum 202from the opening 411, and further inserted into the cylinder 417 fromthe open end of the damper 404, and the front end 413A of the forceimparting member 413 is brought into contact with the sidewall 410. Theforce imparting member 413 is further pushed in the direction of anarrow B. Due to this, the damper 404 moves in the axial direction of theimage carrier drum 202 that is the direction of the arrow B. Even if thedamper 404 is fixed to the inner peripheral surface of the image carrierdrum 202 with an adhesive, the damper 404 can be moved in the directionof the arrow B by thrusting the damper 404 in the direction of the arrowB and breaking the adhesive.

[0293] Thus, by thrusting the force imparting member 413 in thedirection of the arrow B, the sidewall 410 of the damper 404 that movesdue to pressure applied by the force imparting member 413 comes incontact with the second flange 303A and pushes this flange as shown inFIG. 36. Therefore, the flange 303A is separated apart from the imagecarrier drum 202. In this case also, when the flange 303A is fixed tothe image carrier drum 202 with an adhesive, pushing the flange 303Aresults in breaking the adhesive. When the force imparting member 413 ismoved further in the direction of the arrow B, the damper 404 is alsoseparated apart from the image carrier drum 202. Then, the forceimparting member 413 is pulled out from the image carrier drum 202.Thus, the damper 404 and the flange 303A can be separated apart from theimage carrier drum 202 just by pushing the damper 404 by the forceimparting member 413 thereby enabling the disassembling of components ata low cost.

[0294] The damper 404 and the flanges 303 and 303A, having beendisassembled in the above manner, require only cleaning for reuse.Moreover, since the damper 404 before being disassembled is disposed inthe space surrounded by the image carrier drum 202, the flange 303 andthe flange 303A, it is not contaminated by either of dust and tonerduring the use of the image carrier drum 202. Therefore, the damper 404can also be reused without cleaning after it is separated from the imagecarrier drum.

[0295] As explained above, in the method for inserting and removing thedamper into and from the image carrier drum of this example, the damper404 is inserted into the image carrier drum 202 from the opening 411 onone end in the axial direction of the image carrier drum 202. The damper404 is mounted inside the image carrier drum 202 and is removed from theopening 412 on the other end in the axial direction of the image carrierdrum 202. The drum unit 434 includes the image carrier drum 202 and thedamper 404. More specifically, the damper 404 is inserted into the imagecarrier drum 202 from the opening 411 on one end in the axial directionof the drum 202, mounted inside the image carrier drum 202, and thenremoved from the image carrier drum 202 through the opening 412 on theother end in the axial direction of the drum 202.

[0296] Based on the method as explained above, the damper 404 can bemounted inside the image carrier drum 202 or can be removed from thedrum 202 by carrying out simple operation thereby facilitating therecycling process. Only the same operation is required for mounting andremoving the damper 404.

[0297] Besides, according to the method for inserting and removing thedamper into and from the image carrier drum of this example, the damper404 is moved in the axial direction of the image carrier drum 202 byexerting an external force on the damper 404 by the force impartingmember 413 and mounted inside the image carrier drum 202. Similarly, thedamper 404 is moved inside the image carrier drum 202 in its axialdirection by exerting an external force by the force imparting member413 and is removed from the image carrier drum. The damper 404 isapplied with an external force exerted by the force imparting member413, is moved inside the image carrier drum 202 in its axial direction,and is mounted inside the image carrier drum 202. The damper 404 isapplied with an external force exerted by the force imparting member413, is moved inside the image carrier drum 202 in its axial direction,and is removed from the image carrier drum. Thus, operating the forceimparting member 413 enables the damper 404 to be inserted into andremoved from the image carrier drum 202 in a simple manner.

[0298] Moreover, when being inserted into and removed from the imagecarrier drum 202, the damper 404 moves inside the image carrier drum 202in the axial direction of the drum. This direction is simply called amovement direction. The sidewall 410 of the damper 404 is integrated inthe front end of the movement direction of the cylinder 417 of thedamper 404. The force imparting member 413 is in contact and engagedwith the sidewall 410 and pushes the damper. Thus, the sidewall 410 ofthe damper 404 forms an engaging portion with which the force impartingmember 413 is engaged. Hereinafter, reference numeral 401 is assigned tothis engaging portion formed with the sidewall 410.

[0299] As explained above, the damper 404 of this example includes theengaging portion 401 with which the force imparting member 413 isengaged on the front end of the movement direction when the damper 404moves inside the image carrier drum 202 in the axial direction of thedrum 202. The force imparting member 413 exerts an external force on theengaging portion 401 in the direction of movement of the damper 404 andmoves the damper 404 in the axial direction of the image carrier drum202.

[0300] Thus, at least a part of the outer diameter of the damper 404 canbe made to contract by the external force applied by the force impartingmember 413 to the engaging portion 401 in the axial direction of theimage carrier drum 202. Therefore, the damper 404 can be moved smoothlyinside the image carrier drum 202. In other words, the damper 404 shownin the figure is made of an elastic material and the outer diameter ofthe damper 404 before insertion is set to be slightly bigger that theinner diameter of the image carrier drum 202. Therefore, when the damper404 is pushed slightly in the direction of the arrow B by the forceimparting member 413 as shown in FIG. 35, the damper 404 tends to stopfor a while due to the frictional force acting between the innerperipheral surface of the image carrier drum 202 and the outerperipheral surface 414 of the damper 404. However, by further pushingthe engaging portion 401 by the force imparting member 413, the damper404 made of an elastic material tends to be extended in the axialdirection, and the damper 404 undergoes elastic deformation in thedirection of contraction of the diameter as shown by an arrow C in FIG.35. Therefore, the damper 404 can be moved smoothly. Similar deformationoccurs when the damper 404 is pushed out from the image carrier drum.

[0301] When the force imparting member 413 pushes the rear end of thedamper 404 in its axial direction and the damper 404 is made of anelastic material, the frictional force acting between the damper 404 andthe inner peripheral surface of the image carrier drum 202 is exerted onthe damper 404. Therefore, the damper 404 expands in the radial therebyhindering the smooth movement of the damper 404. However, disposing theengaging portion 401 on the front end in the direction of movement ofthe damper 404 prevents such an inconvenience.

[0302] In the example explained above, the damper 404 is pushed by theforce imparting member 413 in the axial direction of the image carrierdrum 202 and is mounted inside the image carrier drum 202. Similarly,the damper 404 is pushed by the force imparting member 413 in the axialdirection and is removed from the image carrier drum 202. The engagingportion 401 of the damper 404 is pushed by the force imparting member413 from one end to the other end of the image carrier drum 202 to movethe damper 404 inside the drum 202.

[0303] On the other hand, an engaging portion of a damper can be pulledby a force imparting member from one end to the other end of the imagecarrier drum 202 to move the damper inside the drum 202. FIG. 38 is across section of an example of how a damper 404 is pulled out from animage carrier drum 202. A sidewall 410 of this damper 404 i.e. anengaging portion 401 has an engagement hole 435. A hook 450A is providedat a front end of a force imparting member 450 which is inserted insidethe image carrier drum 202 through a hole 436 at the center of theflange 303A. The hook 450K is engaged in the engagement hole 435. Bypulling the force imparting member 450 in the direction of an arrow B,the damper 404 can be removed from inside of the image carrier drum 202.In this case as well, the damper 404 pushes the flange 303A, andtherefore the flange 303A can be removed from the image carrier drum202. When the damper 404 is inserted into the image carrier drum 202,with a flange 303 separated apart from the image carrier drum 202, thehook 450A of the force imparting member 450 is engaged in the engagementhole 435 of the damper 404 and the damper 404 is pulled in the directionof the arrow B.

[0304] The rest of the structure other than the drum unit 434 shown inFIG. 38 can also be structured similar to the drum unit explainedearlier. In the case of the drum unit shown in FIG. 38, an externalforce is exerted by the force imparting member 450 on the engagingportion 401 in the axial direction of the image carrier drum 202 tocontract at least a part of the outer diameter of the damper 404.Therefore, the damper 404 can be made to move smoothly inside the imagecarrier drum 202.

[0305] In the example explained above, as a force imparting member thatmoves the damper 404 inside the image carrier drum 202, an exclusivelymade force imparting member 450 (450A) is used. However, as this forceimparting member, a shaft disposed inside the image carrier drum andsupporting the drum can also be used. FIG. 39 is a cross section of anexample of such type of force imparting member. In a drum unit 434 inthe figure, a shaft 437 passes through an image carrier drum 202 and ispress fitted into flanges 330 and 330A. A damper 404 shown in FIG. 39 issimilar to the damper 404 explained in the earlier example. The damper404 in FIG. 39 includes a cylinder 417 that has an outer peripheralsurface fixed to an inner peripheral surface of the image carrier drum202 and a sidewall 410 that is integrated on the front end in themovement direction of the cylinder 417. The sidewall 410 has an engagingportion 401. Moreover, the engaging portion 401 is formed by thesidewall 410 of the damper 404 that is disposed inside the image carrierdrum 202. The engaging portion 401 has a hole 438 having a diameterbigger than that of the shaft 437 that supports the image carrier drum202. The shaft 437 passes through the hole 438.

[0306] The shaft 437 is rotatably supported by the case 219 of theprocess cartridge 218 shown in FIG. 32. The shaft 437 is a component ofthe process cartridge 437. Moreover, the shaft 437 has a bigger diameterportion 439, which can be engaged with the engaging portion 401 of thedamper 404.

[0307] Following is a procedure for assembling the damper 404 inside theimage carrier drum 202. The damper 404 is disposed on the left side ofthe image carrier drum 202 in FIG. 39. The shaft 437 that is without theflanges 303 and 303A fixed is inserted into the drum 202 from theopening on the left end of the drum 202. The shaft 437 is further passedthrough the hole 438 in the damper 404. The engaging portion 401 of thedamper 404 is pushed by the bigger diameter portion 439 of the shaft437, and the damper 404 is pushed in the direction of the arrow B inFIG. 39. While the damper 404 is pushed, the shaft 437 together with thedamper 404 is inserted inside the image carrier drum 202. Then, theflanges 303 and 303A are fitted on the ends of the shaft 437 and also onthe openings at the ends of the image carrier drum 202. Thus, the damper404 is mounted inside the image carrier drum 202.

[0308] When the damper 404 is to be removed from the image carrier drum202, the first flange 303 is pulled out from the shaft 437 first, andthe shaft 437 is made to move in the direction shown by the arrow B inFIG. 39, i.e. in the axial direction of the image carrier drum 202. Thebigger diameter portion 439 of the shaft 437 comes in contact with theengaging portion 401 of the damper 404 and pushes the portion 401 in thedirection of the arrow B. Due to this, the damper 404 moves in the axialdirection of the image carrier drum i.e. in the direction of the arrow Btogether with the shaft 437. When the damper 404 is fixed to the innerperipheral surface of the image carrier drum with an adhesive, thedamper 404 is pushed in the direction of the arrow B thereby breakingthe adhesive to allow the damper 404 to be moved further in thedirection of the arrow B. While doing this, the shaft 437 slides withrespect to the second flange 303A. When the shaft 437 is continued to bemoved in the direction of the arrow B, the damper 404 moving togetherwith the shaft 437 pushes the second flange 303A thereby separating theflange 303A apart from the image carrier drum 202 as shown in FIG. 40.When the shaft 437 is moved further in the direction of the arrow B, thedamper 404 is also separated apart from the image carrier drum 202. Whenthe flange 303A is fitted to the image carrier drum 202 by clearancefit, the flange 303A can also be separated from the image carrier drum202 before the damper 404 comes in contact with the flange 303A.

[0309] The structure can also be made such that the shaft 437 issupported by the main body of the image forming apparatus, the shaft 437is left on the main body of the image forming apparatus, and the drumunit 434 is pulled out from the shaft 437 and can be fitted to the shaft437 again. In such a case, the drum unit 434 is removed from the mainbody of the image forming apparatus. Then, as shown in FIG. 34 to FIG.37, the damper 404 is removed from inside of the image carrier drum 202using an exclusive force imparting member 413, or the damper 404 ismounted inside the drum 202 using the exclusive force imparting member413. Thus, the damper 404 can be easily inserted into and removed fromthe image carrier drum 202.

[0310] The rest of the structure of the drum unit 434 apart from thoseshown in FIG. 39 and FIG. 40 is similar to the structure shown in FIG.32 to FIG. 37.

[0311] The damper 404 can also be formed by a compression coil spring440 as shown in FIG. 41. Due to its elastic nature, the compression coilspring 440 is in pressed contact with the inner peripheral surface ofthe image carrier drum 202. Alternatively, the compression coil spring440 can also be fixed to the inner peripheral surface of the imagecarrier drum 202 with an adhesive.

[0312] The damper 404 formed by the compression coil spring 440 is to beinserted into the image carrier drum 202 by following method. The firstflange 303 is separated from the image carrier drum 202, and a hook 450Aof a force imparting member 450 is engaged with an engaging portion 401Aat one end of the compression coil spring 440. The force impartingmember 450 is pulled in the direction of an arrow B thereby insertingthe damper 404 into the image carrier drum 202 from an opening 411 onone end in the axial direction of the drum 202.

[0313] When the damper 404 formed by the compression coil spring 440 isto be removed, the compression coil spring 440 is pulled by the forceimparting member 450 in the direction of the arrow B in the same manneras explained above. Thus, the damper 404 formed by the compression coilspring 440 can be removed from the image carrier drum 202 through anopening 412 on the other end in the axial direction of the image carrierdrum 202. In this case, the compression coil spring 440 pushes thesecond flange 303A thereby removing the flange 303A from the imagecarrier drum 202. The rest of the structure can be formed similarly tothe example mentioned above. An external force is exerted on theengaging portion 401A in the axial direction of the image carrier drum202 by the force imparting member 450 to reduce at least a part of anouter diameter of the compression coil spring 440, and the compressioncoil spring 440 can be easily moved inside the image carrier drum 202.This action is similar to that in other structures.

[0314] Thus, as mentioned in the examples above, at least a portion ofthe damper that is in contact with the inner wall surface of the imagecarrier drum 202 is formed by an elastic material. The damper 404 makesa pressed contact with the inner wall surface of the image carrier drum202 by the elastic nature i.e. restoring force, and is held inside thedrum 202. When the damper 404 is fixed to the image carrier drum 202without using an adhesive, it can be moved easily in the axial directioninside the image carrier drum 202.

[0315] In the example shown in FIG. 41, when the damper 404 that is tobe removed from the image carrier drum 202 is moved inside the drum 202,the damper 404 pushes the flange 303A fitted on the opening 412 on oneend in the axial direction of the image carrier drum 202 and separatesthe flange 303A apart from the image carrier drum 202. Thus, the flange303 can be separated apart from the image carrier drum 202 just bypushing action by the damper 404, which makes it possible to enhance theworkability.

[0316] When the flange 303A is fitted to the image carrier drum 202 byeither of press fit and clearance fit without using an adhesive, theflange 303A can be removed from the drum 202 when the damper 404 isremoved from the drum 202. The flange 303A can be removed by using asmall amount of force and without any damage caused to it.

[0317] Moreover, as shown in FIG. 42, the second flange 303A can bestructured such that it has a cylindrical first flange member 415 thatfits in the opening 412 at the end in the axial direction of the imagecarrier drum 202 and a second flange member 416 that fits in the firstflange member 415. In this example, a gear 305 is formed on the firstflange member 415. This is similar to the case in the explodedperspective view in FIG. 30. Dimensions of flanges are basically thesame as the dimensions in FIG. 31.

[0318] This structure enables to disengage the second flange member 416from the first flange member 415 using a small amount of force bypushing the second flange member 416 by the damper 404. Thus, the flangemembers 415 and 416 can be separated apart easily from the image carrierdrum 202 without exerting considerable force. This prevents damage tothe first flange member 415 and the second flange member 416 and theseflanges can be reused in the existing condition. This structure can bealso used when the force imparting member is formed by the shaft 437 orwhen the force imparting member is structured as shown in FIG. 38 andFIG. 41.

[0319] As shown in FIG. 42, it is also possible to form at least a part410A of a sidewall 410 of the damper 404 that pushes the second flangemember 416, with a rigid material like metal. Due to such a structure,the force exerted by the force imparting member 413 can be transmitteddirectly to the second flange member 416, and the second flange member416 can be removed easily from the first flange member 415.

[0320] The other structures in the examples shown in FIG. 42 to FIG. 44are similar to the examples explained above.

[0321] In the image forming apparatus shown in FIG. 32, the drum unit434 and the image forming units such as the charging roller 220, thedeveloping unit 222, the cleaning unit 227 which form an image on theimage carrier drum 202 are integrally assembled to the process cartridge218. Therefore, when the process cartridge 218 reaches end of its life,the cartridge may be replaced thereby facilitating maintenance of theimage forming apparatus.

[0322] It is a normal practice to reduce the size and weight of theprocess cartridge to make it easy to handle. Due to use of small sizedcomponents in the process cartridge, the life of the process cartridgeis short. In the image forming apparatus in FIG. 32, an arrangement ismade to replenish the toner container 233 with toner. However, if thereis no such an arrangement for replenishment of the toner and thestructure is made such that the process cartridge is replaced after thedeveloping unit is run out of the toner, the life of the processcartridge becomes further shorter. The short life of the processcartridge implies an increased number of process cartridges that aremade and are in the market. Therefore, it is important to facilitate thedisassembling of the image carrier drum 202, the damper 404, and theflanges 303 and 303A to improve recycling. This can be done in areliable manner by assembling or disassembling the image carrier drum202, the damper 404, and the flanges 303 and 303A as mentioned in theembodiment to enable easy recycling.

[0323] The image forming apparatus shown in FIG. 32 is structured suchthat a transferred toner image can be fixed on the recording medium P atcomparatively low temperature and a toner having a low melting point isused to enable conservation of energy. Concretely, the toner having alow melting point is used in the developing unit to enable the fixing ofthe toner image in the fixing unit at comparatively low surfacetemperature of the fixing roller, for example 145° C. The image formingapparatus forms a toner image on the image carrier drum using a tonerhaving an outflow start temperature less than or equal to 120° C.,preferably in a range of 99° C. to 102° C., measured by flow testermethod. The measurement of outflow start temperature by the flow testermethod is already explained above and hence omitted here.

[0324] A case of using the toner having a low melting point tends togenerate noise easily as compared to a case of using a toner having ahigh melting point. It is not quite sure why the use of the toner havinga low melting point increases the noise. However, It is considered thatadditive like wax contained in the toner tends to stick to the surfaceof the image carrier drum. Since the amount of the additive depositedbecomes non-uniform according to an image pattern, a component like thecleaning blade, which is in contact with the surface of the imagecarrier drum, does not move uniformly. Therefore, it is thought thatloud noise is produced in the image carrier drum due to vibrationscaused by non-uniform movement of the cleaning blade.

[0325] Therefore, it is desirable to use the damper 404 as explainedearlier, which is made of a material having a tangent of loss tan δgreater than or equal to 0.5. The tangent of loss tan δ is a tangent ofa phase angle δ (loss angle) of stress and strain in a material. Thegreater the value of the tangent of loss tan δ, the greater the dampingeffect is. Considering the characteristics of this type of dampingmaterial, the damper 404 made of the material having a tangent of losstan δ greater than or equal to 0.5 is provided inside the image carrierdrum 202 to effectively damp the rotating drum 202. By using the tonerhaving a low melting point, it is possible to reduce the noise generatedin the rotating image carrier drum 202 during image formation to anextremely low level. A rubber material such as butyl rubber and nitrilerubber can be used as a material that has the tangent of loss tan δgreater than or equal to 0.5.

[0326] When a toner including a metallic salt of high fatty acid likezinc stearate is used for the image forming apparatus, a part of thetoner gets deposited on the surface of the image carrier drum 202. Dueto the toner deposited on the surface, the coefficient of friction ofthe cleaning blade 230 decreases thereby smoothening sliding of an edgeof the cleaning blade 230. This reduces vibrations in the cleaning blade230 and improves the prevention of noise considerably.

[0327] The present invention can be applied to an image formingapparatus of any form apart from that mentioned in FIG. 32. It can alsobe applied to an image forming apparatus shown in FIG. 43. In the imageforming apparatus shown in FIG. 43, a charging roller 520 charges animage carrier drum 202 rotating in the direction of an arrow. Thecharged surface of the drum 202 is irradiated with a laser beam Lemitted from an exposing unit (not shown) to form a first electrostaticlatent image on the image carrier drum 202. The electrostatic latentimage is visualized as a yellow toner image by a yellow developingdevice 522Y in the developing unit 522. The yellow toner image is thentransferred to an intermediate transfer belt 550 that is rotating in thedirection of an arrow E. A cleaning unit 527 cleans the surface of theimage carrier drum after transferring of the yellow image.

[0328] Similarly, a second electrostatic latent image is formed on theimage carrier drum 202. The latent image is visualized as a magentatoner image by a magenta developing device 522M in the developing unit522. This toner image is then transferred to the intermediate transferbelt 550 and is superimposed on the yellow toner image, which hasalready been transferred. In a similar way, a cyan toner image and ablack toner image are sequentially formed on the image carrier drum 202by a cyan developing device 522C and a black developing device 522BK inthe developing unit 522 respectively, and these toner images aresuperposedly transferred to the intermediate transfer belt 550.

[0329] The superimposed toner images transferred to the intermediatetransfer belt 550 are then transferred to a recording medium P that isfed from a paper feeding unit 551. When the recording medium passesthrough a fixing unit 552, the toner images are fixed on the recordingmedium.

[0330] A damper 404 is mounted in the image carrier drum 202 of thisimage forming apparatus. The damper 404 is inserted into the imagecarrier drum 202 and then removed in the same manner as explained above.In a case of the image forming unit in FIG. 43, a process cartridge 518can be formed by assembling the image carrier drum 202, at least oneimage forming unit for forming a toner image on the image forming drum,and the intermediate transfer belt 550.

[0331] Thus, the embodiments in which the image carrier drum is formedby a photoreceptor drum are explained above. These structures can alsobe used when the image carrier drum is formed by an intermediatetransfer drum on which a toner image is transferred from thephotoreceptor.

[0332] As explained above, according to the present invention, thevibration absorber is disposed on the side opposite to the surfacefacing the unit in which the bias characteristics for the latent imagecarrier are set. Therefore, due to the bias characteristics, thevibration absorber that is in contact with the latent image carrierabsorbs a part of the vibrations in the latent image carrier, which iscaused by the vibrating electric field generated when ac voltage isapplied. This enables to reduce the resonance in the latent imagecarrier, thereby preventing noise. Even if the latent image carrier iseither of a belt and a thin-walled cylinder in particular, noise can beprevented without increasing the mass and without complicating thestructure of the latent image carrier.

[0333] Further, the vibration absorber is in the form of a roller andthe strong vibration absorbing material is provided either on thesurface of or inside the roller, and therefore even if the roller comesin contact with the latent image carrier, the propagation of vibrationsto the latent image carrier is prevented. Thus, the noise due toresonance in the latent image carrier is prevented.

[0334] Moreover, since the drive roller is used as the vibrationabsorber when the latent image carrier is in the form of a belt, adamper can be used for a material in firm contact with the latent imagecarrier. This facilitates the absorption of vibrations generated in thelatent image carrier and enables to reduce the resonance in the latentimage carrier by using the existing structure.

[0335] When the latent image carrier is a belt, the vibration absorberis provided on the opposite side to the surface of the supporting platewhich is in contact with the latent image carrier. The supporting plateis made of a rigid body in the form of a flat plate and is in contactwith the belt. Therefore, the vibration absorber absorbs the vibrationsgenerated in the belt without obstructing the movement, and resonance inthe latent image carrier can be reduced.

[0336] Since the vibration absorber is disposed in a position oppositeto the unit in which the bias characteristics for the latent imagecarrier are set, the resonance can be reduced in the most efficientmanner at the origin of resonance in the latent image carrier due to thebias characteristics.

[0337] When the latent image carrier is a substrate in the form of athin belt and has a photosensitive layer on the surface of thesubstrate, the substrate is made of a material that absorbs strongvibrations. Therefore, the substrate can reduce it's own vibrations andthere is no need to have a special arrangement for damping and hence noextra cost.

[0338] By setting the value of the tangent of loss tan δ which affectsthe damping effect to be greater than or equal to 0.5, the frequency ofresonance can be changed to the frequency band in which high frequencysound harsh to ears is not produced. Therefore, even when the noise isgenerated from the latent image carrier, the same effect as that ofreducing the noise can be achieved.

[0339] Since the vibration absorber is in the solid cylindrical form, itis possible to change the resonance frequency of the latent imagecarrier to the low frequency band efficiently by using the difference inmass, unlike the hollow cylindrical form. Thus, the resonance caused bythe vibrations of the latent image carrier can be prevented and noisecan be reduced in efficient manner.

[0340] It is possible to reduce the material cost by using the vibrationabsorber in the hollow cylindrical form. In a case of the structure thatleads to the reduction in the material cost, in other words, even in acase where it is difficult to decrease the resonance frequency due tothe mass unlike a case of the solid cylindrical form, deterioration ofthe damping effect can be prevented reliably by setting the value of thetangent of loss tan δ, which affects the damping effect, to be greaterthan or equal to 0.6.

[0341] Moreover, since the vibration absorber is fitted inside thelatent image carrier by either of press fitting and fixing by anadhesive, it is thoroughly integrated with the latent image carrierthereby reducing the resonance in the latent image carrier in efficientmanner.

[0342] The generation of noise can be reduced effectively by using atoner having a low melting point.

[0343] The cylinder unit can be disassembled easily thereby facilitatingrecycling.

[0344] The image carrier drum and the damper can be disassembled easilythereby facilitating recycling.

[0345] The present document incorporates by reference the entirecontents of Japanese priority documents, 2002-169218 filed in Japan onJun. 10, 2002, 2002-170655 filed in Japan on Jun. 11, 2002, 2002-181552filed in Japan on Jun. 21, 2002, 2002-195224 filed in Japan on Jul. 3,2002 and 2003-113709 filed in Japan on Apr. 18, 2003.

[0346] Although the invention has been described with respect to aspecific embodiment for a complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. An image forming apparatus comprising: a latentimage carrier that includes an arrangement of any of a belt and a thinwalled hollow cylinder, the latent image carrier having a first surfaceand a second surface; a bias applying unit that has an arrangement forapproaching towards the first surface of the latent image carrier,wherein the bias applying unit sets bias characteristics of the latentimage carrier; and a vibration absorber that absorbs vibrations in thelatent image carrier, wherein the vibration absorber is made to touchthe second surface of the latent image carrier.
 2. The image formingapparatus according to claim 1, wherein the latent image carrier is thebelt and the vibration absorber is a roller, wherein a surface of theroller is in contact with a surface of the belt, and the surface of theroller is made of a material that absorbs strong vibrations.
 3. Theimage forming apparatus according to claim 1, wherein the latent imagecarrier is the belt and the vibration absorber is a roller, wherein asurface of the roller is in contact with a surface of the belt, and amaterial that absorbs strong vibrations is disposed inside the roller.4. The image forming apparatus according to claim 1, wherein the latentimage carrier is the belt and the vibration absorber is a roller,wherein a surface of the roller is in contact with a surface of thebelt, and the roller drives the belt.
 5. The image forming apparatusaccording to claim 1, wherein the latent image carrier is the belt andthe vibration absorber is a rigid and flat supporting plate, wherein asurface of the plate is in contact with a surface of the belt, and amaterial that absorbs vibrations is provided on a surface of the platethat is on the other side of the surface that makes a contact with thebelt.
 6. The image forming apparatus according to claim 1, wherein thevibration absorber is disposed in a position facing the bias applyingunit.
 7. The image forming apparatus according to claim 1, wherein thelatent image carrier is a thin belt made of a material that absorbsstrong vibrations and the latent image carrier has layer of aphotosensitive material on a surface.
 8. The image forming apparatusaccording to claim 1, wherein a tangent of loss tan δ of the vibrationabsorber is greater than or equal to 0.5, wherein the tangent of loss isa value of damping effect.
 9. The image forming apparatus according toclaim 1, wherein the latent image carrier is the hollow cylinder and thevibration absorber is a solid cylinder that is in contact with an innersurface of the hollow cylinder.
 10. The image forming apparatusaccording to claim 1, wherein the latent image carrier is the hollowcylinder and the vibration absorber is a hollow cylinder that is incontact with an inner surface of the hollow cylinder as the latent imagecarrier.
 11. The image forming apparatus according to claim 10, whereina tangent of loss tan δ of the vibration absorber is greater than orequal to 0.6, wherein the tangent of loss is a value of damping effect.12 The image forming apparatus according to claim 9, wherein the latentimage carrier is the hollow cylinder and the vibration absorber is pressfitted inside the hollow cylinder. 13 The image forming apparatusaccording to claim 10, wherein the latent image carrier is the hollowcylinder and the vibration absorber is press fitted inside the hollowcylinder.
 14. The image forming apparatus according to claim 9, whereinthe latent image carrier is the hollow cylinder and the vibrationabsorber is fixed with an adhesive inside a hollow portion of the hollowcylinder.
 15. The image forming apparatus according to claim 10, whereinthe latent image carrier is the hollow cylinder and the vibrationabsorber is fixed with an adhesive inside a hollow portion of the hollowcylinder.
 16. An image forming apparatus comprising: a toner imageforming unit that forms a toner image on an image carrier drum using atoner having an outflow start temperature less than or equal to 102° C.measured by flow tester method; and a damper provided inside the imagecarrier drum, wherein the damper is made of a material with a tangent ofloss tan δ of the damper is greater than or equal to 0.5, wherein thetangent of loss is a value of damping effect.
 17. The image formingapparatus according to claim 16, wherein the toner contains a metallicsalt of high fatty acid.
 18. The image forming apparatus according toclaim 16, wherein the damper is in a solid cylinder.
 19. The imageforming apparatus according to claim 16, wherein the damper is in ahollow cylinder.
 20. The image forming apparatus according to claim 17,wherein the damper is press fitted inside the image carrier drum. 21.The image forming apparatus according to claim 18, wherein the damper ispress fitted inside the image carrier drum.
 22. The image formingapparatus according to claim 19, wherein the damper is press fittedinside the image carrier drum.
 23. The image forming apparatus accordingto claim 16, wherein the damper is fixed with an adhesive on an innersurface of the image carrier drum.
 24. The image forming apparatusaccording to claim 16, further comprising: a cleaning blade in pressedcontact with a surface of the image carrier drum for cleaning thesurface after the toner image is transferred; and a reverse drivemechanism that rotates the image carrier drum in the direction oppositeto that when the toner image is formed on the image carrier drum. 25.The image forming apparatus according to claim 16, wherein the imagecarrier drum has a protective layer on a surface.
 26. The image formingapparatus according to claim 25, wherein the protective layer contains afiller.
 27. The image forming apparatus according to claim 25, whereinthe protective layer contains a material that carries charge.
 28. Theimage forming apparatus according to claim 16, further comprising: animage forming module that includes at least the image carrier drum and acleaning blade that cleans a surface of the image carrier drum after thetoner image is transferred; and an environment control unit thatcontrols either of temperature and moisture inside the image formingmodule to be less than or equal to a predetermined value.
 29. A drumunit, comprising: a cylinder; a shaft that extends inside and supportsthe cylinder; and a damper disposed inside the cylinder, wherein thecylinder, the shaft, and the damper are assembled such that when theshaft is pulled out from the cylinder, the damper moves in the axialdirection of the cylinder together with the shaft and is removed fromthe cylinder.
 30. The drum unit according to claim 29, wherein the shafthas a protrusion in radial direction and away from a center of theshaft, the damper has a contacting portion that comes in contact withthe protrusion when the shaft is pulled out from the cylinder.
 31. Thedrum unit according to claim 30, wherein the contacting portion is in afront end of the direction of movement of the damper.
 32. The drum unitaccording to claim 29, wherein the damper is coupled together with theshaft such that the damper can move together with the shaft when theshaft is pulled out from the cylinder.
 33. The drum unit according toclaim 29, wherein the mechanism is such that each end in the axialdirection of the cylinder has a pair of flanges fitted respectively, thecylinder is supported by the shaft through these flanges, the dampermoves in the axial direction of the cylinder and comes in contact withone of the flanges, and the flange is separated apart from the cylinderby pushing.
 34. The drum unit according to claim 33, wherein the damperthat comes in contact with the flange is made of a rigid body.
 35. Thedrum unit according to claim 33, wherein the damper that comes incontact with the flange is made of an elastic body.
 36. The drum unitaccording to claim 33, wherein one of the flanges has a first cylindermember that fits at the end of the axial direction of the cylinder, asecond cylinder member fitted in the first cylinder member that pressesthe first cylinder member against an inner wall surface of the cylinder,the damper moves in the axial direction of the cylinder, and a front endsurface of the damper comes in contact with only the second cylindermember out of the two cylinder members and presses the second cylindermember.
 37. The drum unit according to claim 29, wherein the damper isin pressed contact with an inner wall surface of the cylinder and isfixed due to elasticity.
 38. The drum unit according to claim 33,wherein the cylinder, the pair of flanges, and the shaft are assembledtogether to rotate as an integrated assembly.
 39. The drum unitaccording to claim 37, wherein the cylinder, the pair of flanges, andthe shaft are assembled together to rotate as an integrated assembly.40. The drum unit according to claim 29, wherein the cylinder includesan image carrier drum.
 41. An image forming module, comprising: an imagecarrier drum; a shaft that extends inside and supports the drum; adamper disposed inside the drum, wherein the drum, the shaft, and thedamper are assembled such that when the shaft is pulled out from thedrum, the damper moves in the axial direction of the drum together withthe shaft and is removed from the drum; and an image forming elementthat forms an image on the drum, wherein the image carrier drum and theimage forming element are assembled together as an integrated assembly.42. An image forming apparatus comprising: an image carrier drum; ashaft that extends inside and supports the drum; and a damper disposedinside the drum, wherein the drum, the shaft, and the damper areassembled such that when the shaft is pulled out from the drum, thedamper moves in the axial direction of the drum together with the shaftand is removed from the drum.
 43. A method of insertion and removal of adamper into and from an image carrier drum, comprising: inserting thedamper into the image carrier drum from an opening on one end in anaxial direction of the image carrier drum and thereby mounting thedamper inside the drum; and removing the damper from an opening on otherend in the axial direction of the image carrier drum.
 44. The methodaccording to claim 43, wherein the inserting includes moving the damperin the axial direction of the image carrier drum by exerting an externalforce by a force imparting member to thereby mount the damper inside thedrum, and the removing includes moving the damper inside the drum in theaxial direction of the drum by exerting an external force by the forceimparting member to thereby remove the damper from the image carrierdrum.
 45. The method according to claim 44, wherein the force impartingmember is a shaft that is disposed inside the image carrier drum andsupports the image carrier drum.
 46. A drum unit comprising: an imagecarrier drum; and a damper, wherein the damper is inserted into theimage carrier drum from an opening on one end in an axial direction ofthe image carrier drum to thereby mount the damper inside the drum, andthe damper mounted inside the drum is removed from an opening on otherend in the axial direction of the image carrier drum.
 47. The drum unitaccording to claim 46, wherein the damper has elasticity and the damperis held inside the image carrier drum by a pressed contact due to theelasticity with an inner surface of the image carrier drum.
 48. The drumunit according to claim 46, wherein the damper is fixed with an adhesiveon an inner surface of the image carrier drum.
 49. The drum unitaccording to claim 46, further comprising a force imparting member,wherein the damper is moved in the axial direction of the image carrierdrum by exerting an external force by the force imparting member tothereby mount the damper inside the drum, and the damper is moved insidethe drum in the axial direction of the drum by exerting an externalforce by the force imparting member to thereby remove the damper fromthe image carrier drum.
 50. The drum unit according to claim 49, whereinthe damper has an engaging portion at the front end in the direction ofmovement when the damper moves in the axial direction inside the imagecarrier drum, in which the force imparting member engages and the damperis moved in the axial direction of the image carrier drum by theexternal force exerted by the force imparting member on the engagingportion in the direction of movement of the damper.
 51. The drum unitaccording to claim 50, wherein at least a part of an outer diameter ofthe damper is made to contract by the external force exerted by theforce imparting member on the engaging portion in the axial direction ofthe image carrier drum. 52 The drum unit according to claim 50, whereinthe damper is moved inside the image carrier drum by pushing theengaging portion of the damper by the force imparting member from oneend to the other end of the image carrier drum.
 53. The drum unitaccording to claim 50, wherein the damper is moved inside the imagecarrier drum by pulling the engaging portion of the damper by the forceimparting member from one end towards the other end of the image carrierdrum.
 54. The drum unit according to claim 49, wherein the forceimparting member is a shaft that is disposed inside the image carrierdrum and supports the image carrier drum.
 55. The drum unit according toclaim 50, wherein the damper has a cylindrical portion, which has anouter peripheral surface that is fixed with respect to the innerperipheral surface of the image carrier drum; and an edge wall that isintegrated at the front end in the direction of movement of thecylindrical portion and the edge wall is included in the engagingportion.
 56. The drum unit according to claim 55, wherein the engagingportion, which includes the edge wall, has a hole of diameter biggerthan that of a shaft that supports the image carrier drum, and the shaftcan be passed through the hole.
 57. The drum unit according to claim 46,wherein the damper includes a compression coil spring.
 58. The drum unitaccording to claim 46, wherein, the damper that has to be removed fromthe image carrier drum when moved inside the image carrier drum, pushesand separates apart a flange that is fixed on the image carrier drum.59. The drum unit according to claim 58, wherein the flange is fitted tothe drum by either of press fit and clearance fit.
 60. The drum unitaccording to claim 58, wherein the flange includes a first flange memberthat fits in the opening on the other side in the axial direction of theimage carrier drum; and a second flange member that is fitted on thefirst flange member and makes the first flange member to have pressedcontact with the inner peripheral surface of the image carrier drum,wherein a front edge surface of the damper comes in contact with thesecond flange member and pushes the second flange member when the damperthat has to be removed from the image carrier drum is moved inside theimage carrier drum.
 61. An image forming module, comprising: a drum unithaving an image carrier drum; and a damper, wherein the damper isinserted into the image carrier drum from an opening on one end in anaxial direction of the image carrier drum to thereby mount the damperinside the drum, and the damper mounted inside the drum is removed froman opening on other end in the axial direction of the image carrierdrum; and an image forming unit that forms a toner image on the imagecarrier drum, wherein the drum unit and the image forming unit aredetachable from a main body of the image forming apparatus.
 62. An imageforming apparatus comprising an image forming module including a drumunit having an image carrier drum; and a damper, wherein the damper isinserted into the image carrier drum from an opening on one end in anaxial direction of the image carrier drum to thereby mount the damperinside the drum, and the damper mounted inside the drum is removed froman opening on other end in the axial direction of the image carrierdrum; and an image forming unit that forms a toner image on the imagecarrier drum, wherein the drum unit and the image forming unit aredetachable from a main body of the image forming apparatus.
 63. Theimage forming apparatus according to claim 62, wherein the toner imageis formed on the image carrier drum using a toner having outflow starttemperature lower than or equal to 102° C. measured by flow testermethod and the damper is made of a material that has a tangent of losstan δ greater than or equal to 0.5.
 64. An image forming apparatuscomprising a drum unit having an image carrier drum to form a tonerimage; and a damper, wherein the damper is inserted into the imagecarrier drum from an opening on one end in an axial direction of theimage carrier drum to thereby mount the damper inside the drum, and thedamper mounted inside the drum is removed from an opening on other endin the axial direction of the image carrier drum.
 65. The image formingapparatus according to claim 64, wherein the toner image is formed onthe image carrier drum using a toner having outflow start temperaturelower than or equal to 102° C. measured by flow tester method and thedamper is made of a material that has a tangent of loss tan δ greaterthan or equal to 0.5.